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...

Behavioural type systems in programming languages support the specification and verification of properties of programs beyond the traditional use of type systems to describe data processing. A major example of such a property is correctness of communication in concurrent and distributed systems, motivated by the importance of structured communication in modern software.

Behavioural Types: from Theory to Tools presents programming languages and software tools produced by members of COST Action IC1201: Behavioural Types for Reliable Large-Scale Software Systems, a European...