These are the tape recordings of Richard Feynman's 1961-64 Caltech Introductory Physics lectures, which form the basis of the books The Feynman Lectures on Physics and Feynman's Tips on Physics. The original recordings were made on 1/4" reel-to-reel tapes, now preserved in Caltech's Archive. In 2010 the entire collection was digitized by media preservationist George Blood, at a sampling rate of 96 kHz with 24-bit samples, PCM-encoded in WAV files about 2 GB each in size. For this online publication we are serving more compact versions, downsampled to 48 kHz with 16-bit samples, reencoded as AAC-HE (mp4) and Opus (ogg) at a data rate of 48 kbps.

We present entire lecture tapes without any editing or enhancement, including the tape leader. Parts of some lectures edited out of the commercial versions of these recordings are preserved here intact. Recorded material outside the lectures, including discussions between Feynman and his students and/or colleagues, never previously published, can be found in this publication. Three entire lecture recordings never heard before outside Caltech, including two lectures on Quantum Mechanics Feynman gave in 1964, are also included in this publication.¹

I am very excited to at long last be able to share these lecture recordings online, so that everyone can listen to them in their naked beauty. You will hear a lot you have not heard before, in particular, the many "after-lecture" discussions between Feynman and his students, many of which are entertaining and informative.²

Lecture #30 Interference, given on February 20, 1962, is of some historical interest: Feynman delays starting by 6 minutes because earlier that day John Glenn became the first American (and second man, after Yuri Gagarin) to orbit Earth, and he was due to splash down! So, there is a prolonged "before-lecture" discussion in the recording. In the background you can hear the excited hubbub of the students, concerned for Glenn's safe return. Feynman begins his lecture, "Mr. Glenn is in orbit and he'll probably come down during this lecture. We'll see if we get any news from it."

In closing, I wish to thank some people who helped make this publication possible, in particular our publisher Thomas Kelleher at Basic Books, Carver Mead and Adam Cochran at Caltech, and graphic artist Natallia Piatrenka.

The Feynman Lectures Playlist is based on the jQuery plugin jPlayer and jPlayerPlaylist add-on, with several modifications, including the addition of +10 second and -10 second seek hot keys, a playrate control, and persistent playpoints.

The player's controls use standard symbols that are self-explantory. Clicking on a recording in the playlist will select it, and clicking on it a second time will start it playing.

The hot key bindings (for desktops) are described in the following table.

The Read link will take you to the chapter of The Feynman Lectures on Physics or Feynman's Tips on Physics derived from the currently selected recording, and set the playpoint in that chapter's audio player so you can conveniently continue listening while you read.

The Restore link will restore the recording and playpoint that were current the last time you closed or hid the FLP Playlist. You can also do this by loading the FLP Playlist using a special URL,

Bookmark it for convenience.³