This volume contains the proceedings of two international workshops EPEW and WS-FM held atthe Universit ede VersaillesSaint-Quentin-en-Yvelines, V- sailles, France, 1 3 September 2005. EPEW (European Performance Engineering Workshop) and WS-FM (Int- national Workshop on Web Services and Formal Methods) were colocated to gather the researchers working across the spectrum of techniques for modelling, speci?cation, analysis and veri?cation of the behavior of computer systems and business processes. This proceedings contains a selection of 20 research contributions, out of 59 submissions, which...