Published by Prentice Hall in 1985, Communicating Sequential Processes sets out Tony Hoare’s theory of concurrency, developing ideas he had first proposed in a 1978 paper. It became one of the most influential works on how interacting computer processes can be described and understood.

The book presents CSP, a formal notation in which independent processes run in parallel and coordinate by passing messages, synchronising when they communicate. Hoare builds the theory up from simple primitives, using algebraic laws to describe how processes combine, and gives careful attention to problems such as deadlock and non-determinism.

Written with mathematical precision but many worked examples, the book provides a rigorous foundation for reasoning about concurrent and distributed systems. CSP influenced the design of programming languages such as occam, and later Go, and remains a standard reference in the study of concurrency.