In this work, we propose a novel e-Business architecture that takes into account the specific needs of small and medium-sized enterprises (SMEs) and present a modeldriven and highly adaptive approach that facilitates the automation of cross-organizational business processes. Parts of the ebXML standard are leveraged for the initialization of business relationships and for ensuring semantic interoperability, while the Web Services stack builds the technical foundation for the actual execution of transactions. The envisioned architecture comprises active, Web Services-based adapters at the client side to shield technical peculiarities of local IT installations and to ensure seamless collaboration of the diverse stakeholders, but still relies on a central server that enables users to register themselves, to model supported processes and data as well as to negotiate the exact conditions of an electronic business relationship. The resulting approach can thus be considered as hybrid regarding the degree of centralism involved and with respect to the combination of the Web services stack and the ebXML standard as an infrastructural foundation.