The Service-Oriented Architecture promises to be an affordable solution for the integration of heterogeneous systems through the Internet. In the e-Business field, this promise represents a great chance for companies to increase competitiveness and to enable the enactment of new collaborative e-Business processes. In this paper, we present a Virtual Marketplace infrastructure, the VM-Flow, which uses Dynamic Composition of Web Services (Orchestration and Choreography) as a fundamental technique to enable interorganizational business interactions in the context of Dynamic Virtual Enterprises. The VM-Flow platform is workflow-based and also introduces a series of interaction policies to deal with aspects like autonomy and privacy. A platform model is presented together with details on the infrastructure prototype and on an application built over it.1515785