Web services have become a very powerful technology to build service oriented architectures and standardize the access to legacy services. Through web service composition new added value web services can be created out of existing ones. Examples of these compositions are virtual organizations, outsourcing, enterprise application integration, business process definitions and business to business inter/intra-enterprise relationships. In order to enable the construction of business processes as composite web services, a number of composition languages has been proposed by the software industry. However, the handiwork of specifying a business process with these languages through simple text or XML editors is tough, complex and error prone. Visual support can ease the definition of business processes. In this paper, we describe ZenFlow, a visual composition tool for web services written in BPEL4WS. ZenFlow provides several visual facilities to ease the definition of a business process such as multiple views of a process, syntactic and semantic awareness, filtering, logical zooming capabilities and hierarchical representations.