This book constitutes the joint refereed proceedings of the First International Workshop on Theory Building and Formal Methods in Electronic/Mobile Commerce, TheFormEMC, the first European Performance Engineering Workshop, EPEW, and the First International Workshop on Integration of Testing Methodologies, ITM, held jointly in association with FORTE 2004 in Toledo, Spain in October 2004. The 27 revised full papers presented were carefully reviewed and selected from a total of 62 submissions. The papers are grouped in three topical sections corresponding to the workshop topics.