diff --git a/gtk2_ardour/ardour_ui.cc b/gtk2_ardour/ardour_ui.cc
index a23fe35414..07bd90f827 100644
--- a/gtk2_ardour/ardour_ui.cc
+++ b/gtk2_ardour/ardour_ui.cc
@@ -1459,7 +1459,7 @@ ARDOUR_UI::update_disk_space()
 		return;
 	}
 
-	boost::optional<samplecnt_t> opt_samples = _session->available_capture_duration();
+	std::optional<samplecnt_t> opt_samples = _session->available_capture_duration();
 	samplecnt_t fr = _session->sample_rate();
 
 	if (fr == 0) {
diff --git a/gtk2_ardour/axis_view.h b/gtk2_ardour/axis_view.h
index a6e8eec919..3caa3ced87 100644
--- a/gtk2_ardour/axis_view.h
+++ b/gtk2_ardour/axis_view.h
@@ -24,7 +24,7 @@
 #pragma once
 
 #include <list>
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 
 #include <gtkmm/label.h>
 #include <gtkmm/table.h>
@@ -133,6 +133,6 @@ protected:
 	Gtk::Label inactive_label;
 	Gtk::Table inactive_table;
 
-	mutable boost::unordered_map<std::string, std::string> property_hashtable;
+	mutable std::unordered_map<std::string, std::string> property_hashtable;
 }; /* class AxisView */
 
diff --git a/gtk2_ardour/editor.cc b/gtk2_ardour/editor.cc
index a30a2236cb..fb2fdaa2e3 100644
--- a/gtk2_ardour/editor.cc
+++ b/gtk2_ardour/editor.cc
@@ -46,7 +46,6 @@
  * Apple's MacTypes.h and BarController.
  */
 
-#include <boost/none.hpp>
 
 #include <sigc++/bind.h>
 
@@ -1018,7 +1017,7 @@ Editor::deferred_control_scroll (samplepos_t /*target*/)
 {
 	_session->request_locate (*_control_scroll_target);
 	/* reset for next stream */
-	_control_scroll_target = boost::none;
+	_control_scroll_target = std::nullopt;
 	_dragging_playhead = false;
 	return false;
 }
diff --git a/gtk2_ardour/editor.h b/gtk2_ardour/editor.h
index a4622935c2..1e77445dad 100644
--- a/gtk2_ardour/editor.h
+++ b/gtk2_ardour/editor.h
@@ -42,7 +42,7 @@
 #include <string>
 #include <vector>
 
-#include <boost/optional.hpp>
+#include <optional>
 
 #include <gtkmm/comboboxtext.h>
 #include <gtkmm/layout.h>
@@ -532,7 +532,7 @@ private:
 	bool constructed;
 
 	// to keep track of the playhead position for control_scroll
-	boost::optional<samplepos_t> _control_scroll_target;
+	std::optional<samplepos_t> _control_scroll_target;
 
 	SelectionPropertiesBox*      _properties_box;
 
@@ -580,7 +580,7 @@ private:
 
 	void update_join_object_range_location (double);
 
-	boost::optional<float>  pre_notebook_shrink_pane_width;
+	std::optional<float>  pre_notebook_shrink_pane_width;
 
 	Gtk::VBox _editor_list_vbox;
 	Gtk::Notebook _the_notebook;
diff --git a/gtk2_ardour/editor_canvas_events.cc b/gtk2_ardour/editor_canvas_events.cc
index 82be775b44..8871047511 100644
--- a/gtk2_ardour/editor_canvas_events.cc
+++ b/gtk2_ardour/editor_canvas_events.cc
@@ -152,7 +152,7 @@ bool
 Editor::canvas_scroll_event (GdkEventScroll *event, bool from_canvas)
 {
 	if (from_canvas) {
-		boost::optional<ArdourCanvas::Rect> rulers = _time_markers_group->bounding_box();
+		std::optional<ArdourCanvas::Rect> rulers = _time_markers_group->bounding_box();
 		if (rulers && rulers->contains (Duple (event->x, event->y))) {
 			return canvas_ruler_event ((GdkEvent*) event, timecode_ruler, TimecodeRulerItem);
 		}
diff --git a/gtk2_ardour/editor_drag.cc b/gtk2_ardour/editor_drag.cc
index 700a7bfec1..a293e8e556 100644
--- a/gtk2_ardour/editor_drag.cc
+++ b/gtk2_ardour/editor_drag.cc
@@ -1393,7 +1393,7 @@ RegionMotionDrag::motion (GdkEvent* event, bool first_move)
 
 					/* How high is this region view ? */
 
-					boost::optional<ArdourCanvas::Rect> obbox = rv->get_canvas_group ()->bounding_box ();
+					std::optional<ArdourCanvas::Rect> obbox = rv->get_canvas_group ()->bounding_box ();
 					ArdourCanvas::Rect                  bbox;
 
 					if (obbox) {
@@ -5122,7 +5122,7 @@ FeatureLineDrag::motion (GdkEvent*, bool)
 		cx = 0;
 	}
 
-	boost::optional<ArdourCanvas::Rect> bbox = _line->bounding_box ();
+	std::optional<ArdourCanvas::Rect> bbox = _line->bounding_box ();
 	assert (bbox);
 	_line->set (ArdourCanvas::Duple (cx, 2.0), ArdourCanvas::Duple (cx, bbox.value ().height ()));
 
diff --git a/gtk2_ardour/editor_sections.h b/gtk2_ardour/editor_sections.h
index 46c39f37ed..c7a0fa429b 100644
--- a/gtk2_ardour/editor_sections.h
+++ b/gtk2_ardour/editor_sections.h
@@ -19,7 +19,7 @@
 #ifndef _gtk_ardour_editor_sections_h_
 #define _gtk_ardour_editor_sections_h_
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 
 #include "ardour/location.h"
 #include "ardour/session_handle.h"
@@ -108,7 +108,7 @@ private:
 		Gtk::TreeModelColumn<Temporal::timepos_t> end;
 	};
 
-	typedef boost::unordered_map<ARDOUR::Location*, Gtk::TreeModel::iterator> LocationRowMap;
+	typedef std::unordered_map<ARDOUR::Location*, Gtk::TreeModel::iterator> LocationRowMap;
 
 	Columns                      _columns;
 	Glib::RefPtr<Gtk::ListStore> _model;
diff --git a/gtk2_ardour/ghost_event.h b/gtk2_ardour/ghost_event.h
index 5b22a7be54..ed702973b5 100644
--- a/gtk2_ardour/ghost_event.h
+++ b/gtk2_ardour/ghost_event.h
@@ -1,7 +1,7 @@
 #ifndef __gtk2_ardour_ghost_event_h__
 #define __gtk2_ardour_ghost_event_h__
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 #include <sigc++/trackable.h>
 
 #include "evoral/Note.h"
@@ -28,7 +28,7 @@ class GhostEvent : public sigc::trackable
 
 	/* must match typedef in NoteBase */
 	typedef Evoral::Note<Temporal::Beats> NoteType;
-	typedef boost::unordered_map<std::shared_ptr<NoteType>, GhostEvent* > EventList;
+	typedef std::unordered_map<std::shared_ptr<NoteType>, GhostEvent* > EventList;
 
 	static GhostEvent* find (std::shared_ptr<NoteType> parent, EventList& events, EventList::iterator& opti);
 };
diff --git a/gtk2_ardour/midi_view.h b/gtk2_ardour/midi_view.h
index 3dcd95df26..843510f199 100644
--- a/gtk2_ardour/midi_view.h
+++ b/gtk2_ardour/midi_view.h
@@ -28,7 +28,7 @@
 #include <vector>
 #include <stdint.h>
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 
 #include <sigc++/signal.h>
 
@@ -478,9 +478,9 @@ class MidiView : public virtual sigc::trackable, public LineMerger
 	uint8_t get_velocity_for_add (ARDOUR::MidiModel::TimeType time) const;
 	uint8_t get_channel_for_add (ARDOUR::MidiModel::TimeType time) const;
 
-	typedef boost::unordered_map<std::shared_ptr<NoteType>, NoteBase*>                             Events;
-	typedef boost::unordered_map<ARDOUR::MidiModel::PatchChangePtr, std::shared_ptr<PatchChange> > PatchChanges;
-	typedef boost::unordered_map<ARDOUR::MidiModel::constSysExPtr, std::shared_ptr<SysEx> >        SysExes;
+	typedef std::unordered_map<std::shared_ptr<NoteType>, NoteBase*>                             Events;
+	typedef std::unordered_map<ARDOUR::MidiModel::PatchChangePtr, std::shared_ptr<PatchChange> > PatchChanges;
+	typedef std::unordered_map<ARDOUR::MidiModel::constSysExPtr, std::shared_ptr<SysEx> >        SysExes;
 	typedef std::vector<NoteBase*> CopyDragEvents;
 
 	std::shared_ptr<ARDOUR::MidiTrack>   _midi_track;
diff --git a/gtk2_ardour/mixer_group_tabs.cc b/gtk2_ardour/mixer_group_tabs.cc
index f9bf029611..548a5efe33 100644
--- a/gtk2_ardour/mixer_group_tabs.cc
+++ b/gtk2_ardour/mixer_group_tabs.cc
@@ -19,7 +19,6 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <boost/foreach.hpp>
 
 #include "gtkmm2ext/utils.h"
 
@@ -197,7 +196,7 @@ RouteList
 MixerGroupTabs::selected_routes () const
 {
 	RouteList rl;
-	BOOST_FOREACH (AxisView* r, _mixer->selection().axes) {
+	for (AxisView* r : _mixer->selection().axes) {
 		std::shared_ptr<Route> rp = std::dynamic_pointer_cast<Route> (r->stripable());
 		if (rp) {
 			rl.push_back (rp);
diff --git a/gtk2_ardour/mixer_strip.cc b/gtk2_ardour/mixer_strip.cc
index c8c3962b01..4251857e86 100644
--- a/gtk2_ardour/mixer_strip.cc
+++ b/gtk2_ardour/mixer_strip.cc
@@ -1838,24 +1838,24 @@ MixerStrip::parameter_changed (string p)
  *
  *  @return optional value that is present if visibility state should be overridden.
  */
-boost::optional<bool>
+std::optional<bool>
 MixerStrip::override_solo_visibility () const
 {
 	if (is_master ()) {
-		return boost::optional<bool> (false);
+		return std::optional<bool> (false);
 	}
 
-	return boost::optional<bool> ();
+	return std::optional<bool> ();
 }
 
-boost::optional<bool>
+std::optional<bool>
 MixerStrip::override_rec_mon_visibility () const
 {
 	if (is_master ()) {
-		return boost::optional<bool> (false);
+		return std::optional<bool> (false);
 	}
 
-	return boost::optional<bool> ();
+	return std::optional<bool> ();
 }
 
 
diff --git a/gtk2_ardour/mixer_strip.h b/gtk2_ardour/mixer_strip.h
index 42cc7997af..23489ea383 100644
--- a/gtk2_ardour/mixer_strip.h
+++ b/gtk2_ardour/mixer_strip.h
@@ -311,8 +311,8 @@ private:
 	 *  the RC option editor.
 	 */
 	VisibilityGroup _visibility;
-	boost::optional<bool> override_solo_visibility () const;
-	boost::optional<bool> override_rec_mon_visibility () const;
+	std::optional<bool> override_solo_visibility () const;
+	std::optional<bool> override_rec_mon_visibility () const;
 
 	PBD::ScopedConnectionList _config_connection;
 
diff --git a/gtk2_ardour/mixer_ui.cc b/gtk2_ardour/mixer_ui.cc
index 5e646ce867..9c96e26705 100644
--- a/gtk2_ardour/mixer_ui.cc
+++ b/gtk2_ardour/mixer_ui.cc
@@ -33,7 +33,6 @@
 #include <map>
 #include <sigc++/bind.h>
 
-#include <boost/foreach.hpp>
 
 #include <glibmm/threads.h>
 
@@ -3775,7 +3774,7 @@ Mixer_UI::control_action (std::shared_ptr<T> (Stripable::*get_control)() const)
 
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		std::shared_ptr<Stripable> s = r->stripable();
 		if (s) {
 			ac = (s.get()->*get_control)();
@@ -3816,7 +3815,7 @@ Mixer_UI::selected_gaincontrols ()
 {
 	set_axis_targets_for_operation ();
 	ControllableSet rv;
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			std::shared_ptr<GainControl> ac (ms->route()->gain_control());
@@ -3857,7 +3856,7 @@ Mixer_UI::unity_gain_action ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		std::shared_ptr<Stripable> s = r->stripable();
 		if (s) {
 			std::shared_ptr<AutomationControl> ac = s->gain_control();
@@ -3873,7 +3872,7 @@ Mixer_UI::copy_processors ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->copy_processors ();
@@ -3885,7 +3884,7 @@ Mixer_UI::cut_processors ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->cut_processors ();
@@ -3897,7 +3896,7 @@ Mixer_UI::paste_processors ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->paste_processors ();
@@ -3909,7 +3908,7 @@ Mixer_UI::select_all_processors ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->select_all_processors ();
@@ -3921,7 +3920,7 @@ Mixer_UI::toggle_processors ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->toggle_processors ();
@@ -3933,7 +3932,7 @@ Mixer_UI::ab_plugins ()
 {
 	set_axis_targets_for_operation ();
 
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->ab_plugins ();
@@ -3945,7 +3944,7 @@ void
 Mixer_UI::vca_assign (std::shared_ptr<VCA> vca)
 {
 	set_axis_targets_for_operation ();
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->vca_assign (vca);
@@ -3957,7 +3956,7 @@ void
 Mixer_UI::vca_unassign (std::shared_ptr<VCA> vca)
 {
 	set_axis_targets_for_operation ();
-	BOOST_FOREACH(AxisView* r, _axis_targets) {
+	for (AxisView* r : _axis_targets) {
 		MixerStrip* ms = dynamic_cast<MixerStrip*> (r);
 		if (ms) {
 			ms->vca_unassign (vca);
diff --git a/gtk2_ardour/note_base.cc b/gtk2_ardour/note_base.cc
index ffbb9841ee..3392ccf36d 100644
--- a/gtk2_ardour/note_base.cc
+++ b/gtk2_ardour/note_base.cc
@@ -252,7 +252,7 @@ NoteBase::set_mouse_fractions (GdkEvent* ev)
 		return;
 	}
 
-	boost::optional<ArdourCanvas::Rect> bbox = _item->bounding_box ();
+	std::optional<ArdourCanvas::Rect> bbox = _item->bounding_box ();
 	assert (bbox);
 
 	_item->canvas_to_item (ix, iy);
diff --git a/gtk2_ardour/rec_info_box.cc b/gtk2_ardour/rec_info_box.cc
index ca51813429..a7108f59c1 100644
--- a/gtk2_ardour/rec_info_box.cc
+++ b/gtk2_ardour/rec_info_box.cc
@@ -318,7 +318,7 @@ RemainInfoBox::render (Cairo::RefPtr<Cairo::Context> const& cr, cairo_rectangle_
 	}
 
 	samplecnt_t  sample_rate                 = _session->nominal_sample_rate ();
-	boost::optional<samplecnt_t> opt_samples = _session->available_capture_duration ();
+	std::optional<samplecnt_t> opt_samples = _session->available_capture_duration ();
 
 	Gtkmm2ext::set_source_rgb_a (cr, UIConfiguration::instance ().color ("widget:bg"), .7);
 
diff --git a/gtk2_ardour/region_list_base.h b/gtk2_ardour/region_list_base.h
index fa48bc7e92..fc74c196d1 100644
--- a/gtk2_ardour/region_list_base.h
+++ b/gtk2_ardour/region_list_base.h
@@ -22,7 +22,7 @@
 #ifndef _gtk_ardour_region_list_base_h_
 #define _gtk_ardour_region_list_base_h_
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 
 #include <gtkmm/celleditable.h>
 #include <gtkmm/frame.h>
@@ -236,7 +236,7 @@ protected:
 
 	bool _no_redisplay;
 
-	typedef boost::unordered_map<std::shared_ptr<ARDOUR::Region>, Gtk::TreeModel::iterator> RegionRowMap;
+	typedef std::unordered_map<std::shared_ptr<ARDOUR::Region>, Gtk::TreeModel::iterator> RegionRowMap;
 
 	RegionRowMap region_row_map;
 
diff --git a/gtk2_ardour/visibility_group.cc b/gtk2_ardour/visibility_group.cc
index 37c1d5493b..0429f4e82b 100644
--- a/gtk2_ardour/visibility_group.cc
+++ b/gtk2_ardour/visibility_group.cc
@@ -50,7 +50,7 @@ VisibilityGroup::VisibilityGroup (std::string const & name)
  */
 
 void
-VisibilityGroup::add (Gtk::Widget* widget, string const & id, string const & name, bool visible, boost::function<boost::optional<bool> ()> override)
+VisibilityGroup::add (Gtk::Widget* widget, string const & id, string const & name, bool visible, boost::function<std::optional<bool> ()> override)
 {
 	Member m;
 	m.widget = widget;
@@ -92,7 +92,7 @@ bool
 VisibilityGroup::should_actually_be_visible (Member const & m) const
 {
 	if (m.override) {
-		boost::optional<bool> o = m.override ();
+		std::optional<bool> o = m.override ();
 		if (o) {
 			return o.value ();
 		}
diff --git a/gtk2_ardour/visibility_group.h b/gtk2_ardour/visibility_group.h
index 3d01fe58fa..6aa95e0dda 100644
--- a/gtk2_ardour/visibility_group.h
+++ b/gtk2_ardour/visibility_group.h
@@ -41,7 +41,7 @@ public:
 		std::string const &,
 		std::string const &,
 		bool visible = false,
-		boost::function<boost::optional<bool> ()> = 0
+		boost::function<std::optional<bool> ()> = 0
 		);
 
 	Gtk::Widget* list_view ();
@@ -64,7 +64,7 @@ private:
 		std::string  id;
 		std::string  name;
 		bool         visible;
-		boost::function<boost::optional<bool> ()> override;
+		boost::function<std::optional<bool> ()> override;
 	};
 
 	class ModelColumns : public Gtk::TreeModelColumnRecord {
diff --git a/libs/ardour/ardour/disk_reader.h b/libs/ardour/ardour/disk_reader.h
index 212cc39999..ce9d1961e6 100644
--- a/libs/ardour/ardour/disk_reader.h
+++ b/libs/ardour/ardour/disk_reader.h
@@ -22,7 +22,7 @@
 
 #include <atomic>
 
-#include <boost/optional.hpp>
+#include <optional>
 
 #include "evoral/Curve.h"
 
@@ -210,8 +210,8 @@ private:
 	sampleoffset_t        _declick_offs;
 	bool                  _declick_enabled;
 	MidiNoteTracker      _tracker;
-	boost::optional<bool> _last_read_reversed;
-	boost::optional<bool> _last_read_loop;
+	std::optional<bool> _last_read_reversed;
+	std::optional<bool> _last_read_loop;
 
 	static samplecnt_t _chunk_samples;
 
diff --git a/libs/ardour/ardour/disk_writer.h b/libs/ardour/ardour/disk_writer.h
index 9ee8f50687..23f14e90db 100644
--- a/libs/ardour/ardour/disk_writer.h
+++ b/libs/ardour/ardour/disk_writer.h
@@ -22,7 +22,7 @@
 #include <atomic>
 #include <list>
 #include <vector>
-#include <boost/optional.hpp>
+#include <optional>
 
 #include "ardour/disk_io.h"
 #include "ardour/event_ring_buffer.h"
@@ -171,7 +171,7 @@ private:
 
 	samplepos_t get_capture_start_sample_locked (uint32_t n = 0) const;
 
-	boost::optional<samplepos_t> _capture_start_sample;
+	std::optional<samplepos_t> _capture_start_sample;
 
 	samplecnt_t   _capture_captured;
 	bool          _was_recording;
diff --git a/libs/ardour/ardour/playlist.h b/libs/ardour/ardour/playlist.h
index 6a56923ffd..7693f15b1f 100644
--- a/libs/ardour/ardour/playlist.h
+++ b/libs/ardour/ardour/playlist.h
@@ -35,7 +35,7 @@
 
 #include <sys/stat.h>
 
-#include <boost/optional.hpp>
+#include <optional>
 
 #include <glib.h>
 
@@ -471,7 +471,7 @@ private:
 	void coalesce_and_check_crossfades (std::list<Temporal::TimeRange>);
 	std::shared_ptr<RegionList> find_regions_at (timepos_t const &);
 
-	mutable boost::optional<std::pair<timepos_t, timepos_t> > _cached_extent;
+	mutable std::optional<std::pair<timepos_t, timepos_t> > _cached_extent;
 	timepos_t _end_space;  //this is used when we are pasting a range with extra space at the end
 	bool _playlist_shift_active;
 
diff --git a/libs/ardour/ardour/plugin_manager.h b/libs/ardour/ardour/plugin_manager.h
index 5e8d304181..2681433578 100644
--- a/libs/ardour/ardour/plugin_manager.h
+++ b/libs/ardour/ardour/plugin_manager.h
@@ -31,7 +31,6 @@
 #include <map>
 #include <string>
 #include <set>
-#include <boost/container/set.hpp>
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
@@ -193,7 +192,7 @@ private:
 		}
 	};
 
-	typedef boost::container::set<PSLEPtr, PSLEPtrSort> PluginScanLog;
+	typedef std::set<PSLEPtr, PSLEPtrSort> PluginScanLog;
 	PluginScanLog _plugin_scan_log;
 
 	PSLEPtr scan_log_entry (PluginType const type, std::string const& path) {
diff --git a/libs/ardour/ardour/session.h b/libs/ardour/ardour/session.h
index 85a9bb2534..4053206f3f 100644
--- a/libs/ardour/ardour/session.h
+++ b/libs/ardour/ardour/session.h
@@ -768,7 +768,7 @@ public:
 	samplepos_t audible_sample (bool* latent_locate = NULL) const;
 	samplepos_t requested_return_sample() const { return _requested_return_sample; }
 	void set_requested_return_sample(samplepos_t return_to);
-	boost::optional<samplepos_t> const & nominal_jack_transport_sample() { return _nominal_jack_transport_sample; }
+	std::optional<samplepos_t> const & nominal_jack_transport_sample() { return _nominal_jack_transport_sample; }
 
 	bool compute_audible_delta (samplepos_t& pos_and_delta) const;
 	samplecnt_t remaining_latency_preroll () const { return _remaining_latency_preroll; }
@@ -1051,7 +1051,7 @@ public:
 
 	/* s/w "RAID" management */
 
-	boost::optional<samplecnt_t> available_capture_duration();
+	std::optional<samplecnt_t> available_capture_duration();
 
 	/* I/O bundles */
 
@@ -1435,8 +1435,8 @@ private:
 	void add_surround_master ();
 	void remove_surround_master ();
 
-	boost::optional<bool> _vapor_available;
-	boost::optional<bool> _vapor_exportable;
+	std::optional<bool> _vapor_available;
+	std::optional<bool> _vapor_exportable;
 
 	void update_latency (bool playback);
 	void set_owned_port_public_latency (bool playback);
@@ -2317,7 +2317,7 @@ private:
 	CoreSelection* _selection;
 
 	bool _global_locate_pending;
-	boost::optional<samplepos_t> _nominal_jack_transport_sample;
+	std::optional<samplepos_t> _nominal_jack_transport_sample;
 
 	bool _had_destructive_tracks;
 
diff --git a/libs/ardour/ardour/track.h b/libs/ardour/ardour/track.h
index dfb8d1cad0..650b910cb7 100644
--- a/libs/ardour/ardour/track.h
+++ b/libs/ardour/ardour/track.h
@@ -21,7 +21,7 @@
 
 #pragma once
 
-#include <boost/optional.hpp>
+#include <optional>
 #include <memory>
 
 #include "pbd/enum_convert.h"
@@ -196,7 +196,7 @@ protected:
 	void update_input_meter ();
 
 	std::shared_ptr<Playlist>   _playlists[DataType::num_types];
-	boost::optional<MeterPoint> _saved_meter_point;
+	std::optional<MeterPoint> _saved_meter_point;
 	bool                        _record_prepared;
 	TrackMode                   _mode;
 
diff --git a/libs/ardour/ardour/transport_fsm.h b/libs/ardour/ardour/transport_fsm.h
index 4db990d74c..94b660f59f 100644
--- a/libs/ardour/ardour/transport_fsm.h
+++ b/libs/ardour/ardour/transport_fsm.h
@@ -5,7 +5,7 @@
 #include <queue>
 
 #include <boost/intrusive/list.hpp>
-#include <boost/optional.hpp>
+#include <optional>
 
 #include <string>
 #include <utility>
@@ -208,7 +208,7 @@ struct TransportFSM
 	EventList queued_events;
 	EventList deferred_events;
 	int processing;
-	mutable boost::optional<bool> current_roll_after_locate_status;
+	mutable std::optional<bool> current_roll_after_locate_status;
 	mutable double most_recently_requested_speed;
 	mutable double _default_speed;
 	int _reverse_after_declick;
diff --git a/libs/ardour/ardour/transport_master.h b/libs/ardour/ardour/transport_master.h
index 8d2fc37166..48810ae943 100644
--- a/libs/ardour/ardour/transport_master.h
+++ b/libs/ardour/ardour/transport_master.h
@@ -20,7 +20,7 @@
 
 #include <vector>
 
-#include <boost/optional.hpp>
+#include <optional>
 
 #include <glibmm/threads.h>
 #include <glibmm/timer.h>
@@ -152,7 +152,7 @@ public:
 	static std::shared_ptr<TransportMaster> factory (SyncSource, std::string const&, bool removeable);
 	static std::shared_ptr<TransportMaster> factory (XMLNode const&);
 
-	virtual void pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t>) = 0;
+	virtual void pre_process (pframes_t nframes, samplepos_t now, std::optional<samplepos_t>) = 0;
 
 	/**
 	 * This is the most important function to implement:
@@ -513,7 +513,7 @@ public:
 
 	void set_session (Session*);
 
-	void pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t>);
+	void pre_process (pframes_t nframes, samplepos_t now, std::optional<samplepos_t>);
 
 	void unregister_port ();
 
@@ -585,7 +585,7 @@ public:
 
 	void set_session (Session*);
 
-	void pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t>);
+	void pre_process (pframes_t nframes, samplepos_t now, std::optional<samplepos_t>);
 
 	void reset (bool with_pos);
 	bool locked () const;
@@ -666,7 +666,7 @@ public:
 
 	void unregister_port ();
 
-	void pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t>);
+	void pre_process (pframes_t nframes, samplepos_t now, std::optional<samplepos_t>);
 
 	void rebind (MidiPort&);
 
@@ -737,7 +737,7 @@ public:
 	Engine_TransportMaster (AudioEngine&);
 	~Engine_TransportMaster ();
 
-	void pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t>);
+	void pre_process (pframes_t nframes, samplepos_t now, std::optional<samplepos_t>);
 	bool speed_and_position (double& speed, samplepos_t& pos, samplepos_t&, samplepos_t&, samplepos_t);
 
 	bool starting () const
diff --git a/libs/ardour/ardour/transport_master_manager.h b/libs/ardour/ardour/transport_master_manager.h
index 2b6d2772df..8251245140 100644
--- a/libs/ardour/ardour/transport_master_manager.h
+++ b/libs/ardour/ardour/transport_master_manager.h
@@ -117,7 +117,7 @@ class LIBARDOUR_API TransportMasterManager
 	static TransportMasterManager* _instance;
 
 	/* original TC format in case the slave changed it */
-	boost::optional<Timecode::TimecodeFormat> _session_tc_format;
+	std::optional<Timecode::TimecodeFormat> _session_tc_format;
 	void maybe_restore_tc_format ();
 	void maybe_set_tc_format ();
 
diff --git a/libs/ardour/ardour/vst3_plugin.h b/libs/ardour/ardour/vst3_plugin.h
index 9bc671baa5..bffdc462b2 100644
--- a/libs/ardour/ardour/vst3_plugin.h
+++ b/libs/ardour/ardour/vst3_plugin.h
@@ -23,7 +23,7 @@
 #include <set>
 #include <vector>
 
-#include <boost/optional.hpp>
+#include <optional>
 #include <glibmm/threads.h>
 
 #include "pbd/search_path.h"
@@ -328,8 +328,8 @@ private:
 	std::set<Evoral::Parameter> _ac_subscriptions;
 	bool                        _add_to_selection;
 
-	boost::optional<uint32_t> _plugin_latency;
-	boost::optional<uint32_t> _plugin_tail;
+	std::optional<uint32_t> _plugin_latency;
+	std::optional<uint32_t> _plugin_tail;
 
 	int _n_bus_in;
 	int _n_bus_out;
@@ -486,7 +486,7 @@ public:
 	bool                              is_instrument () const;
 	PBD::Searchpath                   preset_search_path () const;
 
-	boost::optional<bool>             has_editor;
+	std::optional<bool>             has_editor;
 
 	std::shared_ptr<VST3PluginModule> m;
 };
diff --git a/libs/ardour/dsp_filter.cc b/libs/ardour/dsp_filter.cc
index d786ac0ab2..cf0adebb4c 100644
--- a/libs/ardour/dsp_filter.cc
+++ b/libs/ardour/dsp_filter.cc
@@ -18,7 +18,6 @@
  */
 
 #include <algorithm>
-#include <boost/math/special_functions/fpclassify.hpp>
 #include <cmath>
 #include <stdlib.h>
 
@@ -135,7 +134,7 @@ LowPass::proc (float* data, const uint32_t n_samples)
 	_z = z;
 	if (!isfinite_local (_z)) {
 		_z = 0;
-	} else if (!boost::math::isnormal (_z)) {
+	} else if (!std::isnormal (_z)) {
 		_z = 0;
 	}
 }
@@ -192,12 +191,12 @@ Biquad::run (float* data, const uint32_t n_samples)
 
 	if (!isfinite_local (_z1)) {
 		_z1 = 0;
-	} else if (!boost::math::isnormal (_z1)) {
+	} else if (!std::isnormal (_z1)) {
 		_z1 = 0;
 	}
 	if (!isfinite_local (_z2)) {
 		_z2 = 0;
-	} else if (!boost::math::isnormal (_z2)) {
+	} else if (!std::isnormal (_z2)) {
 		_z2 = 0;
 	}
 }
diff --git a/libs/ardour/engine_slave.cc b/libs/ardour/engine_slave.cc
index 4f948d7455..a19b7ea161 100644
--- a/libs/ardour/engine_slave.cc
+++ b/libs/ardour/engine_slave.cc
@@ -82,7 +82,7 @@ Engine_TransportMaster::ok() const
 }
 
 void
-Engine_TransportMaster::pre_process (pframes_t, samplepos_t, boost::optional<samplepos_t>)
+Engine_TransportMaster::pre_process (pframes_t, samplepos_t, std::optional<samplepos_t>)
 {
 	/* nothing to do */
 }
diff --git a/libs/ardour/io.cc b/libs/ardour/io.cc
index 8f66ca777f..91141fe5d5 100644
--- a/libs/ardour/io.cc
+++ b/libs/ardour/io.cc
@@ -224,7 +224,7 @@ IO::remove_port (std::shared_ptr<Port> port, void* src)
 	ChanCount after = before;
 	after.set (port->type(), after.get (port->type()) - 1);
 
-	boost::optional<bool> const r = PortCountChanging (after); /* EMIT SIGNAL */
+	std::optional<bool> const r = PortCountChanging (after); /* EMIT SIGNAL */
 	if (r.value_or (false)) {
 		return -1;
 	}
@@ -296,7 +296,7 @@ IO::add_port (string destination, void* src, DataType type)
 	ChanCount after = before;
 	after.set (type, after.get (type) + 1);
 
-	boost::optional<bool> const r = PortCountChanging (after); /* EMIT SIGNAL */
+	std::optional<bool> const r = PortCountChanging (after); /* EMIT SIGNAL */
 	if (r.value_or (false)) {
 		return -1;
 	}
diff --git a/libs/ardour/ltc_slave.cc b/libs/ardour/ltc_slave.cc
index a13f7c9467..8c642485a9 100644
--- a/libs/ardour/ltc_slave.cc
+++ b/libs/ardour/ltc_slave.cc
@@ -564,7 +564,7 @@ LTC_TransportMaster::process_ltc(samplepos_t const now)
 }
 
 void
-LTC_TransportMaster::pre_process (ARDOUR::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+LTC_TransportMaster::pre_process (ARDOUR::pframes_t nframes, samplepos_t now, std::optional<samplepos_t> session_pos)
 {
 	if (!_port) {
 		reset (true);
diff --git a/libs/ardour/midi_clock_slave.cc b/libs/ardour/midi_clock_slave.cc
index f42bbf1051..4843825a88 100644
--- a/libs/ardour/midi_clock_slave.cc
+++ b/libs/ardour/midi_clock_slave.cc
@@ -115,7 +115,7 @@ MIDIClock_TransportMaster::set_session (Session* s)
 }
 
 void
-MIDIClock_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+MIDIClock_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, std::optional<samplepos_t> session_pos)
 {
 	/* Read and parse incoming MIDI */
 	if (!_midi_port) {
diff --git a/libs/ardour/mtc_slave.cc b/libs/ardour/mtc_slave.cc
index afa9318f3b..23a3bd1bea 100644
--- a/libs/ardour/mtc_slave.cc
+++ b/libs/ardour/mtc_slave.cc
@@ -125,7 +125,7 @@ MTC_TransportMaster::set_session (Session* s)
 }
 
 void
-MTC_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+MTC_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, std::optional<samplepos_t> session_pos)
 {
 	/* Read and parse incoming MIDI */
 
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index 57ac1b5644..6db216edba 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -1128,7 +1128,7 @@ Route::add_processors (const ProcessorList& others, std::shared_ptr<Processor> b
 		flags &= mask;
 
 		if (flags != None) {
-			boost::optional<int> rv = PluginSetup (std::dynamic_pointer_cast<Route>(shared_from_this ()), pi, flags);  /* EMIT SIGNAL */
+			std::optional<int> rv = PluginSetup (std::dynamic_pointer_cast<Route>(shared_from_this ()), pi, flags);  /* EMIT SIGNAL */
 			int mode = rv.value_or (0);
 			switch (mode & 3) {
 				case 1:
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index e0f9849a78..1c56aa0778 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -5815,13 +5815,13 @@ Session::graph_reordered (bool called_from_backend)
 /** @return Number of samples that there is disk space available to write,
  *  if known.
  */
-boost::optional<samplecnt_t>
+std::optional<samplecnt_t>
 Session::available_capture_duration ()
 {
 	Glib::Threads::Mutex::Lock lm (space_lock);
 
 	if (_total_free_4k_blocks_uncertain) {
-		return boost::optional<samplecnt_t> ();
+		return std::optional<samplecnt_t> ();
 	}
 
 	float sample_bytes_on_disk = 4.0; // keep gcc happy
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index ef1dd754af..147106993e 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -978,7 +978,7 @@ Session::load_state (string snapshot_name, bool from_template)
 
 		/* there is pending state from a crashed capture attempt */
 
-		boost::optional<int> r = AskAboutPendingState();
+		std::optional<int> r = AskAboutPendingState();
 		if (r.value_or (1)) {
 			state_was_pending = true;
 		} else {
@@ -1717,7 +1717,7 @@ Session::set_state (const XMLNode& node, int version)
 		bool reconfigured = false;
 
 		while (!AudioEngine::instance()->running () || _base_sample_rate != AudioEngine::instance()->sample_rate ()) {
-			boost::optional<int> r = AskAboutSampleRateMismatch (_base_sample_rate, _current_sample_rate);
+			std::optional<int> r = AskAboutSampleRateMismatch (_base_sample_rate, _current_sample_rate);
 			int rv = r.value_or (0);
 			if (rv == 0 && AudioEngine::instance()->running ()) {
 				/* continue with rate mismatch */
@@ -3482,7 +3482,7 @@ struct RegionCounter {
 int
 Session::ask_about_playlist_deletion (std::shared_ptr<Playlist> p)
 {
-	boost::optional<int> r = AskAboutPlaylistDeletion (p);
+	std::optional<int> r = AskAboutPlaylistDeletion (p);
 	return r.value_or (1);
 }
 
@@ -5296,7 +5296,7 @@ Session::save_as (SaveAs& saveas)
 
 					/* tell someone "X percent, file M of N"; M is one-based */
 
-					boost::optional<bool> res = saveas.Progress (fraction, cnt, all);
+					std::optional<bool> res = saveas.Progress (fraction, cnt, all);
 
 					if (res) {
 						keep_going = *res;
diff --git a/libs/ardour/session_transport.cc b/libs/ardour/session_transport.cc
index 02df6e0f59..bd960563fe 100644
--- a/libs/ardour/session_transport.cc
+++ b/libs/ardour/session_transport.cc
@@ -190,7 +190,7 @@ Session::locate (samplepos_t target_sample, bool for_loop_end, bool force, bool
 
 	// Update Timecode time
 	_transport_sample = target_sample;
-	_nominal_jack_transport_sample = boost::none;
+	_nominal_jack_transport_sample = std::nullopt;
 
 	/* Note that loop wrap-around locates do not need to call "seek" */
 	if (force || !for_loop_end) {
diff --git a/libs/ardour/tempo_map_importer.cc b/libs/ardour/tempo_map_importer.cc
index 93c27daa80..ab44173365 100644
--- a/libs/ardour/tempo_map_importer.cc
+++ b/libs/ardour/tempo_map_importer.cc
@@ -87,7 +87,7 @@ bool
 TempoMapImporter::_prepare_move ()
 {
 	// Prompt user for verification
-	boost::optional<bool> replace = Prompt (_("This will replace the current tempo map!\nAre you sure you want to do this?"));
+	std::optional<bool> replace = Prompt (_("This will replace the current tempo map!\nAre you sure you want to do this?"));
 	return replace.value_or (false);
 }
 
diff --git a/libs/ardour/transport_fsm.cc b/libs/ardour/transport_fsm.cc
index d7fb757501..1f99d9d130 100644
--- a/libs/ardour/transport_fsm.cc
+++ b/libs/ardour/transport_fsm.cc
@@ -19,7 +19,6 @@
 
 #include <sstream>
 
-#include <boost/none.hpp>
 
 #include "pbd/error.h"
 #include "pbd/pthread_utils.h"
@@ -104,7 +103,7 @@ TransportFSM::hard_stop ()
 {
 	_motion_state = Stopped;
 	_last_locate.target = max_samplepos;
-	current_roll_after_locate_status = boost::none;
+	current_roll_after_locate_status = std::nullopt;
 	_direction_state = Forwards;
 	_transport_speed = 0;
 	_reverse_after_declick = 0;
@@ -484,7 +483,7 @@ TransportFSM::start_playback ()
 	DEBUG_TRACE (DEBUG::TFSMEvents, "start_playback\n");
 
 	_last_locate.target = max_samplepos;
-	current_roll_after_locate_status = boost::none;
+	current_roll_after_locate_status = std::nullopt;
 
 	if (most_recently_requested_speed == std::numeric_limits<double>::max()) {
 		/* we started rolling without ever setting speed; that's an implicit
@@ -504,7 +503,7 @@ TransportFSM::stop_playback (Event const & s)
 	DEBUG_TRACE (DEBUG::TFSMEvents, "stop_playback\n");
 
 	_last_locate.target = max_samplepos;
-	current_roll_after_locate_status = boost::none;
+	current_roll_after_locate_status = std::nullopt;
 
 	api->stop_transport (s.abort_capture, s.clear_state);
 }
@@ -684,7 +683,7 @@ bool
 TransportFSM::should_roll_after_locate () const
 {
 	bool roll = current_roll_after_locate_status.value_or (api->should_roll_after_locate ());
-	current_roll_after_locate_status = boost::none; // used it
+	current_roll_after_locate_status = std::nullopt; // used it
 
 	DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("should_roll_after_locate() ? %1\n", roll));
 	return roll;
@@ -695,7 +694,7 @@ TransportFSM::roll_after_locate () const
 {
 	bool for_loop = _last_locate.for_loop_end;
 	DEBUG_TRACE (DEBUG::TFSMEvents, string_compose ("rolling after locate, was for_loop ? %1\n", for_loop));
-	current_roll_after_locate_status = boost::none;
+	current_roll_after_locate_status = std::nullopt;
 
 	if (most_recently_requested_speed == std::numeric_limits<double>::max()) {
 		/* we started rolling without ever setting speed; that's an implicit
diff --git a/libs/ardour/transport_master_manager.cc b/libs/ardour/transport_master_manager.cc
index 3c4c645f47..9741c4b3d6 100644
--- a/libs/ardour/transport_master_manager.cc
+++ b/libs/ardour/transport_master_manager.cc
@@ -160,7 +160,7 @@ TransportMasterManager::pre_process_transport_masters (pframes_t nframes, sample
 		return 1.0;
 	}
 
-	boost::optional<samplepos_t> session_pos;
+	std::optional<samplepos_t> session_pos;
 
 	if (_session) {
 		session_pos = _session->audible_sample();
diff --git a/libs/ardour/vst3_host.cc b/libs/ardour/vst3_host.cc
index f690d95a09..7be431c64f 100644
--- a/libs/ardour/vst3_host.cc
+++ b/libs/ardour/vst3_host.cc
@@ -30,7 +30,7 @@
 #endif
 
 #if SMTG_OS_LINUX
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 #include <glibmm.h>
 #endif
 
@@ -102,8 +102,8 @@ private:
 		guint                 _source_id;
 	};
 
-	boost::unordered_map<FileDescriptor, EventHandler> _event_handlers;
-	boost::unordered_map<guint, Linux::ITimerHandler*> _timer_handlers;
+	std::unordered_map<FileDescriptor, EventHandler> _event_handlers;
+	std::unordered_map<guint, Linux::ITimerHandler*> _timer_handlers;
 
 	static gboolean event (GIOChannel* source, GIOCondition condition, gpointer data)
 	{
@@ -132,11 +132,11 @@ public:
 
 	void clear () {
 		Glib::Threads::Mutex::Lock lm (_lock);
-		for (boost::unordered_map<FileDescriptor, EventHandler>::const_iterator it = _event_handlers.begin (); it != _event_handlers.end (); ++it) {
+		for (std::unordered_map<FileDescriptor, EventHandler>::const_iterator it = _event_handlers.begin (); it != _event_handlers.end (); ++it) {
 			g_source_remove (it->second._source_id);
 			g_io_channel_unref (it->second._gio_channel);
 		}
-		for (boost::unordered_map<guint, Linux::ITimerHandler*>::const_iterator it = _timer_handlers.begin (); it != _timer_handlers.end (); ++it) {
+		for (std::unordered_map<guint, Linux::ITimerHandler*>::const_iterator it = _timer_handlers.begin (); it != _timer_handlers.end (); ++it) {
 			g_source_remove (it->first);
 		}
 		_event_handlers.clear ();
@@ -165,7 +165,7 @@ public:
 
 		tresult rv = false;
 		Glib::Threads::Mutex::Lock lm (_lock);
-		for (boost::unordered_map<FileDescriptor, EventHandler>::const_iterator it = _event_handlers.begin (); it != _event_handlers.end ();) {
+		for (std::unordered_map<FileDescriptor, EventHandler>::const_iterator it = _event_handlers.begin (); it != _event_handlers.end ();) {
 			if (it->second._handler == handler) {
 				g_source_remove (it->second._source_id);
 				g_io_channel_unref (it->second._gio_channel);
@@ -198,7 +198,7 @@ public:
 
 		tresult rv = false;
 		Glib::Threads::Mutex::Lock lm (_lock);
-		for (boost::unordered_map<guint, Linux::ITimerHandler*>::const_iterator it = _timer_handlers.begin (); it != _timer_handlers.end ();) {
+		for (std::unordered_map<guint, Linux::ITimerHandler*>::const_iterator it = _timer_handlers.begin (); it != _timer_handlers.end ();) {
 			if (it->second == handler) {
 				g_source_remove (it->first);
 				it = _timer_handlers.erase (it);
diff --git a/libs/audiographer/audiographer/process_context.h b/libs/audiographer/audiographer/process_context.h
index 73528fddb8..4e0b08e74a 100644
--- a/libs/audiographer/audiographer/process_context.h
+++ b/libs/audiographer/audiographer/process_context.h
@@ -1,7 +1,6 @@
 #ifndef AUDIOGRAPHER_PROCESS_CONTEXT_H
 #define AUDIOGRAPHER_PROCESS_CONTEXT_H
 
-#include <boost/static_assert.hpp>
 #include <boost/format.hpp>
 
 #include "audiographer/visibility.h"
@@ -28,7 +27,7 @@ class /*LIBAUDIOGRAPHER_API*/ ProcessContext
 	// This will need to be modified if if it's modified above
 	static const ThrowLevel throwLevel = DEFAULT_THROW_LEVEL;
 
-	BOOST_STATIC_ASSERT (std::is_trivially_destructible<T>::value);
+	static_assert (std::is_trivially_destructible<T>::value);
 
 public:
 
diff --git a/libs/audiographer/audiographer/type_utils.h b/libs/audiographer/audiographer/type_utils.h
index a022d48d45..0dee5386a5 100644
--- a/libs/audiographer/audiographer/type_utils.h
+++ b/libs/audiographer/audiographer/type_utils.h
@@ -1,7 +1,6 @@
 #ifndef AUDIOGRAPHER_TYPE_UTILS_H
 #define AUDIOGRAPHER_TYPE_UTILS_H
 
-#include <boost/static_assert.hpp>
 #include <memory>
 #include <algorithm>
 #include <cstring>
@@ -30,7 +29,7 @@ class LIBAUDIOGRAPHER_API TypeUtilsBase
 template<typename T = DefaultSampleType>
 class /*LIBAUDIOGRAPHER_API*/ TypeUtils : private TypeUtilsBase
 {
-	BOOST_STATIC_ASSERT (std::is_trivially_destructible<T>::value);
+	static_assert (std::is_trivially_destructible<T>::value);
 
 	typedef std::bool_constant<std::is_floating_point<T>::value ||
 	                           std::is_signed<T>::value> zero_fillable;
diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 55432e5857..6578242f44 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -24,7 +24,6 @@
 
 #include <glibmm.h>
 
-#include <boost/foreach.hpp>
 #include <boost/tokenizer.hpp>
 
 #include "alsa_audiobackend.h"
@@ -1002,7 +1001,7 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 
 		boost::tokenizer<boost::char_separator<char> > devs (ext, sep);
 
-		BOOST_FOREACH (const std::string& tmp, devs) {
+		for (const std::string& tmp : devs) {
 			std::string            dev (tmp);
 			unsigned int           sr     = _samplerate;
 			unsigned int           spp    = _samples_per_period;
diff --git a/libs/canvas/canvas/meter.h b/libs/canvas/canvas/meter.h
index e3ca56351d..41a2c3d5a2 100644
--- a/libs/canvas/canvas/meter.h
+++ b/libs/canvas/canvas/meter.h
@@ -20,8 +20,7 @@
 #define __push2_meter_h__
 
 #include <map>
-#include <boost/tuple/tuple.hpp>
-#include <boost/tuple/tuple_comparison.hpp>
+#include <tuple>
 
 #include <cairomm/pattern.h>
 #include <cairomm/region.h>
@@ -156,9 +155,9 @@ class Meter : public Item {
 				|| (dim == rhs.dim && stp == rhs.stp && cols < rhs.cols)
 				|| (dim == rhs.dim && stp == rhs.stp && cols == rhs.cols && style < rhs.style);
 		}
-		boost::tuple<int, int> dim;
-		boost::tuple<float, float, float, float> stp;
-		boost::tuple<int, int, int, int, int, int, int, int, int, int> cols;
+		std::tuple<int, int> dim;
+		std::tuple<float, float, float, float> stp;
+		std::tuple<int, int, int, int, int, int, int, int, int, int> cols;
 		int style;
 	};
 	typedef std::map<Pattern10MapKey, Cairo::RefPtr<Cairo::Pattern> > Pattern10Map;
@@ -172,8 +171,8 @@ class Meter : public Item {
 		inline bool operator<(const PatternBgMapKey& rhs) const {
 			return (dim < rhs.dim) || (dim == rhs.dim && cols < rhs.cols) || (dim == rhs.dim && cols == rhs.cols && (sh && !rhs.sh));
 		}
-		boost::tuple<int, int> dim;
-		boost::tuple<int, int> cols;
+		std::tuple<int, int> dim;
+		std::tuple<int, int> cols;
 		bool sh;
 	};
 	typedef std::map<PatternBgMapKey, Cairo::RefPtr<Cairo::Pattern> > PatternBgMap;
diff --git a/libs/canvas/test/arrow.cc b/libs/canvas/test/arrow.cc
index 2be958c6db..1f9ecc94fd 100644
--- a/libs/canvas/test/arrow.cc
+++ b/libs/canvas/test/arrow.cc
@@ -27,7 +27,7 @@ ArrowTest::bounding_box ()
 
 	arrow.set_outline_width (0);
 
-	boost::optional<Rect> bbox = arrow.bounding_box ();
+	std::optional<Rect> bbox = arrow.bounding_box ();
 
 	CPPUNIT_ASSERT (bbox.is_initialized ());
 	CPPUNIT_ASSERT (bbox.value().x0 == -6);
diff --git a/libs/canvas/test/group.cc b/libs/canvas/test/group.cc
index a6d7d8de54..a9b7c6bdd3 100644
--- a/libs/canvas/test/group.cc
+++ b/libs/canvas/test/group.cc
@@ -23,7 +23,7 @@ GroupTest::bounding_box ()
 	c.set_outline_width (0);
 	Rectangle d (canvas.root(), Rect (33, 33, 64, 64));
 	d.set_outline_width (0);
-	boost::optional<Rect> bbox = canvas.root()->bounding_box ();
+	std::optional<Rect> bbox = canvas.root()->bounding_box ();
 
 	/* check the bounding box */
 	CPPUNIT_ASSERT (bbox.is_initialized ());
@@ -51,7 +51,7 @@ GroupTest::null_bounding_box ()
 
 	Group empty (canvas.root());
 
-	boost::optional<Rect> bbox = empty.bounding_box ();
+	std::optional<Rect> bbox = empty.bounding_box ();
 	CPPUNIT_ASSERT (!bbox.is_initialized ());
 }
 
@@ -116,7 +116,7 @@ GroupTest::children_changing ()
 	a.set_outline_width (0);
 
 	/* Check that initial bbox */
-	boost::optional<Rect> bbox = canvas.root()->bounding_box ();
+	std::optional<Rect> bbox = canvas.root()->bounding_box ();
 	CPPUNIT_ASSERT (bbox.is_initialized ());
 	CPPUNIT_ASSERT (bbox.value().x0 == 0);
 	CPPUNIT_ASSERT (bbox.value().y0 == 0);
@@ -156,7 +156,7 @@ GroupTest::grandchildren_changing ()
 	a.set_outline_width (0);
 
 	/* Check the initial bboxes */
-	boost::optional<Rect> bbox = canvas.root()->bounding_box ();
+	std::optional<Rect> bbox = canvas.root()->bounding_box ();
 	CPPUNIT_ASSERT (bbox.is_initialized ());
 	CPPUNIT_ASSERT (bbox.value().x0 == 0);
 	CPPUNIT_ASSERT (bbox.value().y0 == 0);
@@ -276,7 +276,7 @@ GroupTest::torture_add_items_at_point ()
 		}
 
 		for (list<Item*>::iterator j = rectangles.begin(); j != rectangles.end(); ++j) {
-			boost::optional<Rect> bbox = (*j)->bounding_box ();
+			std::optional<Rect> bbox = (*j)->bounding_box ();
 			assert (bbox);
 			if (bbox.value().contains (test)) {
 				items_B.push_back (*j);
diff --git a/libs/canvas/test/polygon.cc b/libs/canvas/test/polygon.cc
index d117bb9223..ff9ce6a1b9 100644
--- a/libs/canvas/test/polygon.cc
+++ b/libs/canvas/test/polygon.cc
@@ -29,7 +29,7 @@ PolygonTest::bounding_box ()
 	/* should now have a bounding box around those points,
 	   taking into account default line width
 	*/
-	boost::optional<Rect> bbox = polygon.bounding_box ();
+	std::optional<Rect> bbox = polygon.bounding_box ();
 	CPPUNIT_ASSERT (bbox.is_initialized ());
 	CPPUNIT_ASSERT (bbox.value().x0 == -6.25);
 	CPPUNIT_ASSERT (bbox.value().x1 ==  6.25);
diff --git a/libs/canvas/test/types.cc b/libs/canvas/test/types.cc
index ba6baef149..1f5d97a2b9 100644
--- a/libs/canvas/test/types.cc
+++ b/libs/canvas/test/types.cc
@@ -12,7 +12,7 @@ TypesTest::intersect ()
 	{
 		Rect a (0, 0, 1024, 1024);
 		Rect b (0, 0, 512, 512);
-		boost::optional<Rect> c = a.intersection (b);
+		std::optional<Rect> c = a.intersection (b);
 
 		CPPUNIT_ASSERT (c.is_initialized ());
 		CPPUNIT_ASSERT (c->x0 == 0);
@@ -24,7 +24,7 @@ TypesTest::intersect ()
 	{
 		Rect a (0, 0, 512, 512);
 		Rect b (513, 513, 1024, 1024);
-		boost::optional<Rect> c = a.intersection (b);
+		std::optional<Rect> c = a.intersection (b);
 
 		CPPUNIT_ASSERT (!c.is_initialized ());
 	}
diff --git a/libs/midi++2/mtc.cc b/libs/midi++2/mtc.cc
index 25d118372e..053a23b9c2 100644
--- a/libs/midi++2/mtc.cc
+++ b/libs/midi++2/mtc.cc
@@ -185,7 +185,7 @@ Parser::process_mtc_quarter_frame (MIDI::byte *msg)
 			   true, just ignore this in terms of it being an error.
 			*/
 
-			boost::optional<bool> res = mtc_skipped ();
+			std::optional<bool> res = mtc_skipped ();
 
 			if (res.value_or (false)) {
 
diff --git a/libs/midi++2/parser.cc b/libs/midi++2/parser.cc
index da75aec248..9907d48b09 100644
--- a/libs/midi++2/parser.cc
+++ b/libs/midi++2/parser.cc
@@ -325,7 +325,7 @@ void
 Parser::scanner (unsigned char inbyte)
 {
 	bool statusbit;
-        boost::optional<int> edit_result;
+        std::optional<int> edit_result;
 
 	// cerr << "parse: " << hex << (int) inbyte << dec << " state = " << state << " msgindex = " << msgindex << " runnable = " << runnable << endl;
 
@@ -393,7 +393,7 @@ Parser::scanner (unsigned char inbyte)
 	}
 
 	if (rtmsg) {
-		boost::optional<int> res = edit (&inbyte, 1);
+		std::optional<int> res = edit (&inbyte, 1);
 
 		if (res.value_or (1) >= 0 && !_offline) {
 			realtime_msg (inbyte);
@@ -430,7 +430,7 @@ Parser::scanner (unsigned char inbyte)
 #endif
 		if (msgindex > 0) {
 
-			boost::optional<int> res = edit (msgbuf, msgindex);
+			std::optional<int> res = edit (msgbuf, msgindex);
 
 			if (res.value_or (1) >= 0) {
 				if (!possible_mmc (msgbuf, msgindex) || _mmc_forward) {
diff --git a/libs/pbd/pbd/signals.h b/libs/pbd/pbd/signals.h
index 8143e005a9..880489fd5f 100644
--- a/libs/pbd/pbd/signals.h
+++ b/libs/pbd/pbd/signals.h
@@ -38,7 +38,7 @@
 #include <boost/bind/protect.hpp>
 #include <boost/function.hpp>
 #include <boost/enable_shared_from_this.hpp>
-#include <boost/optional.hpp>
+#include <optional>
 
 #include "pbd/libpbd_visibility.h"
 #include "pbd/event_loop.h"
@@ -87,7 +87,7 @@ template<typename R>
 class /*LIBPBD_API*/ OptionalLastValue
 {
 public:
-	typedef boost::optional<R> result_type;
+	typedef std::optional<R> result_type;
 
 	template <typename Iter>
 	result_type operator() (Iter first, Iter last) const {
diff --git a/libs/surfaces/console1/console1.cc b/libs/surfaces/console1/console1.cc
index 7e8c4cfc23..282da7d1ec 100644
--- a/libs/surfaces/console1/console1.cc
+++ b/libs/surfaces/console1/console1.cc
@@ -16,7 +16,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#include <boost/optional.hpp>
+#include <optional>
 
 #include "pbd/abstract_ui.cc" // instantiate template
 #include "pbd/controllable.h"
@@ -1112,7 +1112,7 @@ void
 Console1::create_strip_inventory ()
 {
 	DEBUG_TRACE (DEBUG::Console1, "create_strip_inventory()\n");
-	boost::optional<order_t> master_order;
+	std::optional<order_t> master_order;
 	strip_inventory.clear ();
 	StripableList sl = session->get_stripables ();
 	uint32_t index = 0;
diff --git a/libs/surfaces/websockets/dispatcher.h b/libs/surfaces/websockets/dispatcher.h
index 2928b82443..1d2d9d4c39 100644
--- a/libs/surfaces/websockets/dispatcher.h
+++ b/libs/surfaces/websockets/dispatcher.h
@@ -19,7 +19,7 @@
 #ifndef _ardour_surface_websockets_dispatcher_h_
 #define _ardour_surface_websockets_dispatcher_h_
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 
 #include "client.h"
 #include "component.h"
@@ -39,7 +39,7 @@ public:
 
 private:
 	typedef void (WebsocketsDispatcher::*DispatcherMethod) (Client, const NodeStateMessage&);
-	typedef boost::unordered_map<std::string, DispatcherMethod> NodeMethodMap;
+	typedef std::unordered_map<std::string, DispatcherMethod> NodeMethodMap;
 
 	static NodeMethodMap _node_to_method;
 
diff --git a/libs/surfaces/websockets/server.h b/libs/surfaces/websockets/server.h
index cc2cc77d1c..2dceb5f2fb 100644
--- a/libs/surfaces/websockets/server.h
+++ b/libs/surfaces/websockets/server.h
@@ -19,7 +19,7 @@
 #ifndef _ardour_surface_websockets_server_h_
 #define _ardour_surface_websockets_server_h_
 
-#include <boost/unordered_map.hpp>
+#include <unordered_map>
 #include <glibmm.h>
 #include <libwebsockets.h>
 
@@ -63,7 +63,7 @@ private:
 	struct lws_context_creation_info  _lws_info;
 	struct lws_context*               _lws_context;
 
-	typedef boost::unordered_map<Client, ClientContext> ClientContextMap;
+	typedef std::unordered_map<Client, ClientContext> ClientContextMap;
 	ClientContextMap                                    _client_ctx;
 
 	ServerResources _resources;
@@ -90,7 +90,7 @@ private:
 
 	Glib::RefPtr<Glib::IOChannel> _channel;
 
-	typedef boost::unordered_map<lws_sockfd_type, LwsPollFdGlibSource> LwsPollFdGlibSourceMap;
+	typedef std::unordered_map<lws_sockfd_type, LwsPollFdGlibSource> LwsPollFdGlibSourceMap;
 	LwsPollFdGlibSourceMap _fd_ctx;
 
 	bool _fd_callbacks;
diff --git a/libs/widgets/widgets/fastmeter.h b/libs/widgets/widgets/fastmeter.h
index f7cc53ccc7..cde924ce31 100644
--- a/libs/widgets/widgets/fastmeter.h
+++ b/libs/widgets/widgets/fastmeter.h
@@ -21,8 +21,7 @@
 #define _WIDGETS_FAST_METER_H_
 
 #include <map>
-#include <boost/tuple/tuple.hpp>
-#include <boost/tuple/tuple_comparison.hpp>
+#include <tuple>
 #include <cairomm/pattern.h>
 #include "gtkmm2ext/cairo_widget.h"
 
@@ -143,9 +142,9 @@ private:
 				|| (dim == rhs.dim && stp == rhs.stp && cols < rhs.cols)
 				|| (dim == rhs.dim && stp == rhs.stp && cols == rhs.cols && style < rhs.style);
 		}
-		boost::tuple<int, int> dim;
-		boost::tuple<float, float, float, float> stp;
-		boost::tuple<int, int, int, int, int, int, int, int, int, int> cols;
+		std::tuple<int, int> dim;
+		std::tuple<float, float, float, float> stp;
+		std::tuple<int, int, int, int, int, int, int, int, int, int> cols;
 		int style;
 	};
 	typedef std::map<Pattern10MapKey, Cairo::RefPtr<Cairo::Pattern> > Pattern10Map;
@@ -159,8 +158,8 @@ private:
 		inline bool operator<(const PatternBgMapKey& rhs) const {
 			return (dim < rhs.dim) || (dim == rhs.dim && cols < rhs.cols) || (dim == rhs.dim && cols == rhs.cols && (sh && !rhs.sh));
 		}
-		boost::tuple<int, int> dim;
-		boost::tuple<int, int> cols;
+		std::tuple<int, int> dim;
+		std::tuple<int, int> cols;
 		bool sh;
 	};
 	typedef std::map<PatternBgMapKey, Cairo::RefPtr<Cairo::Pattern> > PatternBgMap;
diff --git a/libs/widgets/widgets/frame.h b/libs/widgets/widgets/frame.h
index d6650f011c..b30d4d677e 100644
--- a/libs/widgets/widgets/frame.h
+++ b/libs/widgets/widgets/frame.h
@@ -19,7 +19,7 @@
 #ifndef _WIDGETS_FRAME_H_
 #define _WIDGETS_FRAME_H_
 
-#include <boost/optional.hpp>
+#include <optional>
 #include <gtkmm/bin.h>
 
 #include "gtkmm2ext/colors.h"
@@ -65,7 +65,7 @@ private:
 	sigc::connection            _parent_style_change;
 	Glib::RefPtr<Pango::Layout> _layout;
 	std::string                 _label_text;
-	boost::optional<Gdk::Color> _edge_color;
+	std::optional<Gdk::Color> _edge_color;
 	GtkRequisition              _min_size;
 
 	int  _border;