Electronic marketplaces represent a significant example for the evolution of the Internet from technical infrastructure to business enabler. Built on top of open standards like XML and value-added services like catalogue, negotiation, and transaction management, electronic marketplaces are the new hubs for business interaction. In first-generation electronic marketplaces service providers post information about their products, and service consumers post information about their needs. The matching is based on a market-dependent ontology, and standardised negotiation processes are supported by market mechanisms like auctions and exchanges. The final result is a one-to-one business relationship managed directly by the parties, outside the boundaries of the electronic marketplace. For second- generation electronic marketplaces the focus shifts on complete solutions. The capability to aggregate multiple services in order to match a specific service request should be provided as an internal service from electronic marketplaces. As an alternative, the electronic marketplaces should at least enable specific service providers to sustain effectively aggregation-oriented business models. After an overview of electronic marketplaces, we introduce the concept of e-services as electronic virtualisation of standard business services. We then present DySCo (Dynamic Service Composer), which includes a model and a reference infrastructure for e-service management and composition. Based on DySCo, a prototype has been developed for dynamic service aggregation through negotiation in multiple marketplaces. The prototype is presented, and the implications of the underlying business model are discussed. 17 Pages