It is generally agreed between researchers and practitioners that user involvement is a key to the success of computer based information systems. This paper treats user involvement within the framework of a dyadic (two party) communication relationship between user and specialist. We add to previous work in three respects. First, the theoretical framework is enriched by specifying what we consider to be important contingency factors for the interaction between user and specialist. Second, a formal theory for predicting the success of information system development projects is developed. Third, one important managerial tool to establish effective user-specialist communication is suggested.