This book constitutes the refereed proceedings of two colocated international workshops EPEW 2005 (European Performance Engineering Workshop) and WS-FM 2005 (Web Services and Formal Methods) held in Versailles, France in September 2005.The 20 revised full papers presented were carefully reviewed and selected from 59 submissions. For EPEW 2005 only 10 papers - of the 32 submitted - were accepted for presentation; they deal with queueing theory, bounding techniques, stochastic model checking, communication schemes analysis for high-speed LAN, QOS analysis in wireless ad-hoc networks and optical networks analysis. The main topics of the 10 papers accepted for WS-FM 2005 - from 27 submissions - include: protocols and standards for WS (SOAP, WSDL, UDDI, etc.); languages and description methodologies for Choreography/Orchestration/Workflow (BPML, XLANG and BizTalk, WSFL, WS-BPEL, etc.); coordination techniques for WS (transactions, agreement, coordination services, etc.); semantics-based dynamic WS discovery services (based on Semantic Web/Ontology Techniques or other semantic theories); security, performance evaluation and quality of service of WS; semi-structured data and XML related technologies; comparisons with different related technologies/approaches.