This article describes the development of the Comprehensive Assessment of Team Member Effectiveness. The authors used the teamwork literature to create potential items, which they tested using two surveys of college students (Ns = 2,777 and 1,157). The authors used exploratory factor analysis and confirmatory factor analysis to help them select items for the final instrument. The full instrument has 87 items that measure 29 types of team member contributions with 3 items each. These fall into five categories (contributing to the team's work; interacting with teammates; keeping the team on track; expecting quality; and having relevant knowledge, skills, and abilities). A short version of the instrument has 33 items. Potential uses for the instrument and suggestions for future research are discussed. Sources of the Initial Pool of Items is appended. (Contains 3 tables.)