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 in?uential 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 ?rst 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, re?ect upon and look beyondthe?rstquarter-centuryof CSP’scontributionstocomputerscience. The meeting examined the impact of CSP on many areas stretching from semantics (mathematical models for understanding concurrency and communications) and logic(forreasoningaboutbehavior), throughthedesignofparallelprogramming 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 Ph D students and others, featured a ?re alarm (requ- ing evacuation in the rain!) and concluded with the presentation of a fountain pen to Prof. Sir C. A. R. Hoare.