This special issue covers the following areas of business processes: semantics and analysis of process models, process simulation, and process execution. In the first paper, "Process Instantiation", Decker & Mendling examine alternative ways to define the instantiation semantics of process models, particularly in the context of languages in which the models may have multiple start events. In the second paper, Vanhatalo et al. define a canonical representation of process models, namely the "Refined Process Structure Tree" (RPST). The RPST of a process model is a hierarchy of sub-processes, each with a single entry and a single exit point. The third paper, "Deciding Service Composition and Substitutability Using Extended Operating Guidelines" by Stahl and Wolf, investigates open issues in the field of service protocol analysis. Next, Rozinat et al. propose an integrated approach that seamlessly links workflow execution with workflow simulation. In the final paper, "RESTful Web Service Composition with BPEL for REST'', the author proposes an extension of the BPEL standard in order to support the composition of RESTful Web services.