This book constitutes the thoroughly refereed post-proceedings of the 8th International Workshop on Web Services and Formal Methods, WS-FM 2011, held in Clermont-Ferrand, France, in September 2011. The workshop was co-located with the 9th International Conference on Business Process Management, BPM 2011. The 9 full papers presented were carefully reviewed and selected from 14 submissions. They deal with service oriented computing (SOC), cloud computing and formal methods.