SOA and web services are supposed to increase integration capabilities, stimulate inter-organizational processes, and thereby improve coordination in distributed business networks. They also foster the idea of dynamic business networks with quick connect and disconnect relationships. While service-oriented concepts are increasingly adopted in practice, they are still mostly applied within company boundaries. Little research has systematically analyzed how SOA is applied in inter-organizational relationships and business networks. In addition, SOA concepts are not yet sufficiently linked to the mature stream of research on inter-organizational information systems (IOS). Hence, we lack a more fundamental understanding of how SOA impacts business networks. Our research aims at filling this gap. First, we propose a multi-dimensional classification scheme for assessing SOA adoption in business networks. This scheme is derived from inter-organizational systems (IOS), SOA and business networking literature. Second, we analyze 25 inter-organizational SOA cases to identify focus areas and patterns of SOA adoption in business networks. Third, we compare our findings to the propositions from SOA and IOS literature. While our empirical analysis does not confirm all enthusiastic propositions related to SOA, it underlines the specific contribution of SOA compared to prior forms of IOS.