All 20 volumes in THE FEYNMAN LECTURES ON PHYSICS: THE COMPLETE AUDIO COLLECTION by Richard Feynman and produced Perseus books. Recordings are on cassettes, 6 cassettes per lecture. Volumes 1- 4 have been opened and presumably listened to. They are in very good condition. Volumes 5-20 are still in plastic wrap and unopened as new. Recordings are unabridged. Please email me if you have any questions.