In recent years, industrial relations scholars have begun to discuss the 'revitalisation strategies' unions are using to rebuild lost density, power, and political leverage. This thesis studies the role international activities play in the revitalisation of Australian unions. Rather than assert the importance of international activity, or emphasise the value of certain forms of international activity, the thesis seeks to understand why unions choose to engage in particular forms of international activity. International activity in Australian unions takes on a remarkable diversity of forms. The analysis of international activity therefore requires a theory that is capable of describing these different forms of international activity and then explaining why they exist. However most scholars have not examined the role of union agency in choosing international activity. Within industrial relations, there is very little existing theory or research on which to base the kind of analysis proposed for the thesis. Most theories are ideologically driven, prescriptive accounts that either promote or challenge particular institutions or ideas about international activity. The problem is that they deal with international activity as an abstract kind of response to universal pressures of globalisation. These kinds of arguments serve well to articulate the need for unions to 'think globally', but are ill suited to the task of the thesis, which is to explain particular forms of international activity in particular unions. The questions about international activity that the thesis intends to answer form a point of connection between industrial relations and the related discipline of labour geography. In making the connections between labour geography theory and the analysis of union international strategy, the thesis argues for labour geography as a political economic foundation for industrial relations in the tradition of Hyman's Marxist theory of industrial relations. This provides a critical theoretical perspective and conceptual vocabulary with which to criticise and extend industrial relations research on international activity. The result is a spatialised theory organised according to topics of interest in industrial relations research that can be applied to the study of Australian international activity. The thesis is evenly divided between developing this theory and research on international activity in the Australian union movement. Empirical analysis begins with a study of the international activities and policy of the ACTU, distinguishing different kinds of international activity. By treating the international activities of the ACTU as representative of the Australian union movement as a whole, the thesis identifies three functional levels of international activity: strategy-sharing, regional solidarity, and global regulation. The chapter also examines the material and discursive construction of the international scale within the ACTU. The thesis also analyses the international activities of three Australian unions,the TWU, LHMU and CFMEU. While all three unions engage in each level of international activity, the review of their activities shows differences in the focus of each union. The thesis suggests that the explanation for these different ratios depends in part on the spatial structure of the industries that the different unions organise. The kind of research undertaken in this thesis has little precedent. The work of the labour geographers on international activity does not deal with union revitalisation strategy, and the research from industrial relations on the strategic aspects of international activity have not latched on to labour geography. This thesis argues that unions scale their activities internationally for particular reasons, some of which are structural and can be specified up front, and others that are historically contingent and can only be explored on a case-by-case basis. In examining this 'politics of scale' the thesis redefines many of the issues in the discussion of international activity and proposes a new conceptual background for industrial relations generally.