In an age of globalised, highly competitive, volatile and financialised markets, the question of how to effectively organise workers to win concrete improvements in their working lives is increasingly difficult to answer. This thesis builds on four years of action-research, which supported eight unions in one company spread across five countries, to coordinate some of their actions and to push for a Global Framework Agreement to secure workers’ associational freedoms. It highlights the difficulties that workers face when trying to collaborate across borders and argues that any attempt to effectively study or empower trade unions at the scale of their multinational employer must pay attention to the specific factors which condition their agency as well as to the goals, tactics and enactments through which the ideal of international solidarity is embodied. The company studied produces silicon chips, employing approximately 28,000 workers across highly capital-intensive processes of research, development and chip production in the Global North, alongside 17,000 workers in the Global South to test and assemble the circuits. Between 2005 and 2016, the company underwent a process of financialisation, distributing ever larger dividends to its shareholders, whilst decreasing capital expenditure and implementing several restructuring and layoff plans. Faced with what they saw as an existential threat to their company’s future, seven unions from four different countries (France, Italy, Morocco and Malaysia) organised successful joint actions to secure greater capital investments and the replacement of the corporation’s senior management team. Following this campaign, these unions, joined by an eighth from Malta, created an international network to exchange information and campaigned without success for the company to sign a Global Framework Agreement. This attempt to organise across sites, languages, cultures, and institutional contexts, I argue, acts as a microcosm of the difficulties workers face in their efforts to exert power in a world characterised by globalising and centralising production and intensified financialisation. This thesis makes two contributions to labour geography and struggles for workers’ rights more broadly. First, it argues that any attempt to understand these struggles and their chances of success must be attuned to the actually-existing conditions of building solidarity and that these conditions cross a number of spatialities and temporalities. The unions’ international solidarity efforts were balanced on a series of contradictory and uneven relationships. Their members were tied to specific national interests, and their company confronted heightened pressures of scale which reverberated across the sites. Each union reflected their members’ experiences and socio-spatial positionalities, whose register crossed a number of scales and each union was threatened and/or co-opted by corporate tactics and stood by different ideological visions. Unless scholars and activists attend to these detailed variations and stories, practices and studies of international labour solidarity will remain an abstract ideal, rather than placed in the grounded and ‘messy’ attempt by workers’ organisations to deal with and work across multiple differences. Second, it argues that international efforts which focus on formal processes of rule-making at the expense of more grassroots and militant approaches stifle international collaboration. To sustain international collaboration, instead of an institutional and “dialogue”- based approach, which underplays the conflict opposing workers and their employers, trade unions should push for ambitious demands based on shared experiences and interests and engage in truly reciprocal forms of solidarity, rather than semi-patronising “help” models, whilst recognising that these discussions are traversed by each unions’ local realities and ideological stances. Ultimately, this thesis reminds us that building a sense of collective agency at the international scale is an iterative process, necessary but difficult, facing constant threats and changing circumstances. In the face of a global economy managed with increasing disregard for workers’ dignity and survival, let alone their power, it is vital that geographers pay increased attention to the strategies, challenges, and achievements of unions both on the ground, and, even if unsuccessful, over space.