It is a well-known problem that small and medium size enterprises (SMEs) have difficulty to participate in electronic commerce. In particular, the SME participation in business-to-business electronic commerce is seriously lagging behind compared to the very active participation of large companies. We discuss several barriers that could explain why SMEs have problems to participate in electronic commerce. Examples of such barriers range from lack of trust because of unclear status of electronic trade documents to specific SME problems in back office processing of electronic (EDI) messages. We also present a generic architecture that is specifically dedicated to improve the participation by solving these barriers for SME participation.