Business-to-business e-contracting aims at automating the contracting process between companies. It improves the efficiency of the contracting process and enables the introduction of new business models that can be supported by companies. For the development of an e-contracting system, an architecture is required that describes the system components and the communication channels between them. This paper presents a reference architecture for the development of e-contracting systems. The architecture is designed on the basis of a requirement analysis of e-contracting systems. Established architectural principles are used in its design. The architecture can serve as a foundation in the analysis and design of concrete architectures of e-contracting systems. Furthermore, it can be used as a standardization model that facilitates system integration and communication of ideas. Its value for both software architects and business professionals makes it an important tool in the analysis and implementation of e-contracting systems.