The CSP approach has been widely used in the specification, analysis and verification of concurrent and real–time systems, and for understanding the particular issues that can arise when concurrency is present. It provides a language which enables specifications and designs to be clearly expressed and understood, together with a supporting theory which allows them to be analysed and shown to be correct. This book supports advanced level courses on concurrency covering timed and untimed CSP. The first half introduces the language of CSP, the primary semantic models (traces, failures, divergences and infinite traces), and their use in the modelling, analysis and verification of concurrent systems. The second half of the book introduces time into the language, brings in the timed semantic model (timed failures) and finally presents the theory of timewise refinement which links the two halves together. Author's Website containing:∗ Exercises and solutions∗ Instructor's resources∗ Example CSP programs to run on FDR and ProBe∗ Links to useful sites