Web Services and Formal Methods

This volume contains the papers presented at WS-FM 2009: The 6th Inter- tional Workshop on Web Services and Formal Methods held during September 4-5, 2009 in Bologna, Italy. There were 18 submissions by authors from 12 countries. Each submission was reviewed by at least 3, and on the average 3.9, Program Committee m- bers. The committee decided to accept 10 papers. Most of the selected papers are reports on work in progress on problems related to formal aspects of Web services. This workshop also features three invited talks by Mariangiola Dezani (Sessions and Session Types: An Overview), Robin Milner (Processes, and C- egories of Bigraphs) and Maurizio Lenzerini. Dezani's talk is included in this volume. We thank all authors who submitted papers to this workshop, and the m- bersof the ProgramCommittee for their workin the reviewprocess.We arealso grateful to the CONCUR 2009 organizers who take care of many organizational details for the workshop and, in particular, to Mario Bravetti and Gianluigi - vattaro. We also thank EasyChair that helped us in the management of every step of the workshop.