This paper presents an overview of the literature on union commitment. The aim is to survey the main approaches, findings and implications of the research. The nature and dimensionality of union commitment are examined, and the antecedents and consequences of union commitment are discussed in detail, including a review of the implications for union participation. There is also a discussion of the possibility of dual commitment to union and employer, and of the ‘multiple constituencies’ view of commitment. An attempt is made to link the union commitment findings to the wider industrial relations literature on, for example, why people join unions and the ‘union renewal’ thesis. The article concludes by discussing the implications of the literature for union–management relationships and for unions themselves, and with some suggestions for future research.