Service-oriented architectures promise flexible process integration in heterogeneous environments, particularly in cross organizational contexts. Therefore, a systematic approach for deriving service definitions from cross-organizational business processes is required. The paper at hand presents a structured, model driven approach that allows for cross-organizational integration with service-oriented concepts and technologies based on a cross-organizational business process. The resulting method is specified by means of a metamodel and a procedure model. Taking into account existing approaches in the research field, the paper focuses on the activities for the service design specification and the subsequent implementation of the public services. Feasibility of the method is shown by applying it in a Business-to-Government (B2G) real-world scenario, namely the collaboration between a consigning company and customs authorities according to the new European harmonized customs procedures.