This book constitutes the thoroughly refereed post-workshop proceedings of the 9th International Workshop on Web Services and Formal Methods, WS-FM 2012, held in Tallinn, Estonia, in September 2012. The 9 papers presented were carefully reviewed and selected from 19 submissions. They cover aspects such as the modeling and analysis of web services, service discovery, and service coordination with formal methods like BPEL, CSP, Maude, and Petri nets.