The definition and the management of business processes are considered a relevant issue to support organizations in their activities. Indeed, in the last few years many organizations have been changing their business processes to keep competitive in the global market. Workflow management is an emerging technology enabling process performance improvement in a cooperative working environment. In particular, a workflow management system (WfMS) enables processes automation through the integration, the coordination, and communication of both human and automatic task of business processes. WfMSs provide a process definition language (PDL) for modeling business processes. A PDL sentence is named process model and is enacted by a component of the WfMS, namely the process engine. The main task of this component is executing the enactment rules and the activities specified in the Process Model. A huge number of PDLs based on several formalisms have been proposed in literature. Recently, some authors suggest exploiting the unified modeling language (UML) proposed by the Object Management Group (OMG, 2002) to model business processes (Aversano, Canfora, De Lucia, & Gallucci, 2002; Di Nitto, Lavazza, Schiavoni, Tracanella, & Trombetta, 2002; Eriksson & Penker, 2000, Jager, Schleicher, & Westfechtel, 1999; Marshall, 2000). UML is a natural choice for representing business processes, as it is a well known notation that can be easily understood and used by any kind of users. In this article, we propose a Web services-based WfMS that lets users manage and enact business processes. The proposed system offers a visual environment based on an extension of UML activity diagrams that allows to graphically design a process model and to visually monitor its enactment. Since UML does not have a well defined operational semantics and is not executable, we had to make the process model executable by appropriately enriching the syntax and semantics of UML activity diagrams. The architecture of the proposed WfMS is based on Web services to manage and enact distributed business processes.