Understanding the factors influencing information system IS effectiveness has been of considerable concern to IS researchers, with the role of user participation UP in IS success receiving much attention. The inconclusive and often contradictory research results in this area of inquiry have been attributed to a lack of rigor in method and to the lack of consideration of various intervening mechanisms between UP and IS success. This paper develops a model to explain a potential link of UP with IS success; the model is based upon a synthesis of UP and IS success research coupled with principles of attribution theory. Attribution theory is the study of the process by which people associate causes to outcomes or events. This theory implies the need to consider IS users' causal attributions for the IS-related outcomes they experience, as the nature of these attributions will likely influence users' evaluation of the IS. In synthesizing IS and attribution theory, this paper proposes that users' causal attributions of success and failure subsequent to IS use, is one factor explaining the linkages between UP, beliefs, and IS success. It is argued that UP is a critical determinant of IS success to the extent that it influences beliefs that lead to users' attributions for IS related outcomes, and ultimately to their subjective evaluation and future use of the IS. Consequently, a model is proposed that permits a more meaningful examination of the role of UP in IS success.