What we have here is John Cage, Karlheinz Stockhausen, Toshi Ichiyanagi, Morton Feldman, Robert Ashley, the recently late and great Pauline Olivers, Christian Wolff, Dick Higgins, Steve Reich and so forth. The talent doesn't stop! Each issue had a focus on one or two composers and a specific work by them, as well as dialogue / interviews with specific composers. Also manifestos of all sorts, and even a dip into politics. My understanding is that finding a copy of "Source" is nearly impossible, and I can see why. Why would anyone want to give up their copy?
This book is an important and incredible source for music that was produced in the years from 1966 thru 1973. A casual reader would for sure want to check out a composer's work, just by reading what that work is/was. Also a lot of the new music at that time was very theatrical and performance friendly. Towards the end of the book one gets a great sample of works by the Fluxus artists/performers. Highly entertaining, this book is essential for either those who study the arts that were produced during that time period, but also the importance and greatness of new music of that time.