An increasing level of cooperation between public administrations nowadays on national, regional and local level requires methods to develop interoperable EGovernment systems and leads to the necessity of an efficient modeling of collaborative business processes and their implementation. In this paper a framework to systematically develop interoperable systems in the public sector is described. The methodology is motivated and explained on the basis of an E-Government reference model for the German Plan Approval Procedure. In this context it is described how cross-organizational business processes can be modeled and transformed to technical process models in the form of Web Service protocols. After a motivation for the need of interoperability frameworks and a description of related work, section 3 introduces the methodical interoperability framework. Further detailing the contents of this framework, section 4 presents a method for the creation of collaborative business processes on a...