The Session is the fundamental document type that is created and modified by the Ardour workstation. A Session is a folder on a computer filesystem that contains all the items that pertain to a particular project or "recording/editing/mixing session".

The Session folder includes these files and folders:

• session_name.ardour the main session snapshot
• *.ardour, any additional snapshots
• session_name.ardour.bak, the auto-backup snapshot
• session_name.history, the undo history for the session
• instant.xml, which records the last-used zoom scale and other metadata
• interchange/, a folder which holds the raw audio and MIDI files (whether imported or recorded)
• export/, a folder which contains any files created by the Session > Export function
• peaks/, a folder which contains waveform renderings of all audio files in the session
• analysis/, a folder which contains transient and pitch information of each audio file that has been analysed
• dead sounds/, a folder which contains sound files which Ardour has detected are no longer used in the session (during a Session > Clean-up > Clean-up Unused Sources operation, will be purged by Flush Waste Basket, see Cleaning Up Sessions)

A session combines some setup information (such as audio and MIDI routing, musical tempo & meter, timecode synchronization, etc.) with one or more Tracks and Buses, and all the Regions and Plug-Ins they contain.

Ardour supports loading session files created with older versions of the program. The oldest known version is 2.8 released in 2009. With very few exceptions, Ardour will load all session data from such files. The data that cannot be supported (e.g. the old way of storing region fades) will be skipped entirely.