A marketplace as a historically-evolved institution allows customers and suppliers to meet at a certain place and a certain time in order to announce buying or selling intentions which eventually match and may be settled. Due to the evolution of communication technologies time and space restrictions have been weakened. Electronic markets (EM) representing the next step in the evolution of the former marketplace. They are emerging in different fields, supporting the exchange of goods and services of different types, with different types of actors and are following different architectural principles. Some of the existing new systems are solutions for just parts of the transaction process which do not inter-operate with other systems. Further, the Internet with its tremendous evolution fosters the development of EM in retail business. A lot of different EM will arise which have to co-operate and network with each other. This rather hinders a structured development of EM and demands for common architectural principles. The necessity for a reference model towards real EM is given.