Industry standards for Web Service composition, such as WSBPEL, provide the notation and additional control mechanisms for the execution of business processes in Web Service collaborations. However, these standards do not provide support for checking interesting properties related to Web Service and process behaviour. In an attempt to fill this gap, we describe a formalization of WSBPEL business processes, that adds protocol information to the specifications of interacting Web Services, and uses a process algebra to model their dynamic behaviour -- thus enabling their formal analysis and the inference of relevant properties of the systems being built. Key words: Web Services, orchestration, WSBPEL, formal methods, process algebra, interoperability, adaptation.