Why do some teams fail to convert members' knowledge into valued outcomes? We propose that members' differing perceptions of each other's levels of expertise is a critical factor. To capture this phenomenon, we introduce the concept of expertise dissensus, a team property that reflects the variance in team members' perceptions of one another's levels of expertise. We argue that it matters how team members perceive all others' expertise - not just how they view the most expert team member -and develop and test a multi-level model to explain how expertise dissensus affects team processes and outcomes. We further advance theory by investigating the effects of expertise dissensus on all dimensions of team effectiveness: team performance, team viability, and individual member development (Hackman, 1987).