This volume contains the refereed joint proceedings of two initiatives that have been devoted to the formal foundations of complex systems: the workshops WS-FM:FASOCC 2014 and WS-FM/BEAT 2015.

The 11th International Workshop on Web Services and Formal Methods: Formal Aspects of Services-Oriented and Cloud Computing, WS-FM 2014, took place in Eindhoven, The Netherlands, in September 2014. The 12th International Workshop on Web Services, Formal Methods, and Behavioral Types, WS-FM 2015, took place in Madrid, Spain, in September 2015.

The total of 8 papers presented in this volume was carefully reviewed and selected from 18 submissions. They were organized in topical sections named: expressiveness of behavioral models; service-oriented systems, and behavioral types.