This Thesis presents an overview of the literature on union commitment, identifies some key research gaps and questions, and reports eight empirical papers that attempt to address some of the gaps in the literature. The empirical work involves eleven separate studies of union commitment in the UK, Hong Kong and mainland Peoples Republic of China in public sector services (nursing, healthcare professionals, fire-fighting, teaching and the civil service), private sector services (windscreen repair, water utilities) and private sector manufacturing (food processing, engine manufacturing, forging). The research overview aims to survey the main approaches, findings and implications of the extant research on union commitment. The nature dimensionality, antecedents and especially the consequences of union commitment are identified and examined in detail. A particular theme examines the implications of union commitment for members' active participation in their unions. The thesis examines the possibility of dual commitment to unions and employing organizations and the "multiple constituencies" view of employee commitment. An attempt is made to link up the empirical findings of the research to the wider industrial relations literature, for example on why workers join unions, and key debates such as union renewal and revitalisation. The implication of the findings on union commitment are examined in relation to the union-management relationship and future union strategy. The research has important policy implications for the organizing-servicing debate as a way for forward for trade unions.