The International Astronomical Union Colloquium on Stellar Rotation was held at the Ohio State University in Columbus, Ohio, U.S.A. from September 8th through 11 th, 1969. Forty-four scientists from Argentina, Belgium, Canada, England, Finland, East and West Germany, Italy, Israel, Japan, The Netherlands, and the United States attended and participated in the Colloquium. The present volume, which parallels the actual program closely, contains the papers presented at the Colloquium plus most of the discussion following those papers. The Colloquium was sponsored by the International Astronomical Union, the Ohio State University, and the National Science Foundation. It is a pleasure to record my thanks to these organizations and especially to Dr. Geoffrey Keller, Dean of the College of Mathematics and Physical Sciences of the Ohio State University, and to Prof. C. de Jager, Assistant General Secretary of the International Astronomical Un­ ion, for their kind cooperation. I am also grateful to H. A. Abt, J. Hardorp, R. P. Kraft, Mrs. A. Massevitch, M. Plavec, 1. W. Roxburgh, and E. Schatzman of the Organizing Committee, as well as A. J. Deutsch and G. W. Collins, II, for their help in planning the Colloquium­ all of them offered valuable suggestions toward organizing the program.