One cannot build or understand a modern operating system unless one knows the principles of concurrent programming. This volume is a collection of 19 original papers on the invention and origins of concurrent programming, illustrating the major breakthroughs in the field from the mid 1960s to the late 1970s. All of them are written by the pioneers in concurrent programming, including Brinch Hansen himself, and have introductions added that summarize the papers and put them in perspective. This anthology is an essential reference for professional programmers, researchers, and students of electrical engineering and computer science. A familiarity with operating system principles is assumed.