This volume, like the symposium CSP25 which gave rise to it, commemorates the semi-jubilee of Communicating Sequential Processes. 1 Tony Hoare’s paper “Communicating Sequential Processes” is today widely regarded as one of the most influential papers in computer science. To comm- orate it, an event was organized under the auspices of BCS-FACS (the British Computer Society’s Formal Aspects of Computing Science specialist group). CSP25 was one of a series of such events organized to highlight the use of formal methods, emphasize their relevance to modern computing and promote their wider application. BCS-FACS is proud that Tony Hoare presented his original ideas on CSP at one of its first meetings, in 1978. The two-day event, 7–8 July 2004, was hosted by London South Bank U- versity’s Institute for Computing Research, Faculty of Business, Computing and Information Management. The intention was to celebrate, reffect upon and look beyondthe first quarter-century of CSP’s contributions computer science. The meeting examined the impact of CSP on many areas stretching from semantics (mathematical models for understanding concurrency and communications) and logic (for reasoning about behavior), through the design of parallel programming languages (i/o, parallelism, synchronization and threads) to applications va- ing from distributed software and parallel computing to information security, Web services and concurrent hardware circuits. It included a panel discussion with panelists Brookes, Hoare, de Roever and Roscoe (chaired by Je? Sanders), poster presentations by PhD students and others, featured a fire alarm (requ- ing evacuation in the rain!) and concluded with the presentation of a fountain pen to Prof. Sir C. A. R. Hoare.