The raising need for e-government applications leads to many new approaches in this sector. To fulfill the requirement for a flexible government-to-government (G2G) software system being adaptable for the usage in many sectors of e-government applications we introduce the reference architecture for e-government (RAfEG) in this paper. The key features of the system are flexibility, security, adaptability and interoperability between authorities. The efficient usage of heterogeneous systems and heterogeneous hardware platforms, respectively, allows the execution of large interactive applications in e-government. Because security is a critical issue in e-government applications our solution uses different types of authentication and authorization methods and also supports secure communication between the interoperating heterogeneous systems. Due to the fact that the electronically supported execution of government procedures is the main aspect of the RAfEG system, an approach where these procedures are modeled as workflows and executed by an underlying workflow management system (WfMS) is the solution we present in this paper. Although many e-government applications exist at present, the RAfEG system is a new approach because it is able to cope with a wide range of internal official procedures and also highly adaptable to new procedures within e-government.