Trade union free-riding is a highly contentious issue for trade unions. Yet, it is poorly understood. Using data from a representative survey this article examines the incidence of free-riding in Ireland and profiles those who free-ride, distinguishing between two cohorts – never-have-been union members and former union members. The authors examine a series of hypotheses derived from the international literature to assess how free-riders are distinguished from union members and, in turn, how the two cohorts of free-riders are dissimilar from one another in their orientations to unions. The article concludes by identifying a number of theoretical contributions, makes some suggestions for the conduct of future research and identifies a number of policy implications for unions.