The nature and extent of members’ commitment to their labor union has been a topic of research interest for approximately 75 years. Although the rationale for studying member commitment has varied across the years, union commitment has emerged as a central variable in understanding union_member relations and, by extension, the process of unionization. The purpose of this chapter is to: (1) provide a brief review of the history and development of the construct of union commitment; (2) examine the current state of knowledge regarding the predictors, consequences, and correlates of union commitment; and (3) to re-evaluate the operational measures of union commitment and offer the outline of a research agenda that is intended to reinvigorate the study of union commitment.