'This book on session types, one of most fruitful and successful topics in concurrency theory over the past 30 years, is written with great clarity, deep insight, and enthusiasm by two of most renowned researchers in the field. It is a most welcomed text, both for learning from and for teaching. It offers a comprehensive account of the basic theory and explains the possible applications, beautifully leavened with insightful examples and exercises. It will become -- and well deserves to become - the definitive reference textbook on session types.' Davide Sangiorgi, University of Bologna