Information systems development (ISD) projects are complex, requiring a variety of expertise. Coordinating such expertise helps manage complexity, increasing the likelihood of a project's success. Findings of past studies have been inconsistent regarding the benefits of expertise coordination—perhaps, in part, because three different forms of coordination have been used: willingness, ability, and behavior. We find that willingness and ability are antecedents of coordination behavior, and that coordination behavior fully mediates different forms of project success. Thus, successful expertise coordination requires team members who are both willing and able. The implications and limitations of this study are discussed.