The paper explores processes of social movement learning within SINTRAEMCALI, a public service trade union in the South West of Colombia, which has successfully prevented a series of attempts by the national government to privatise public utilities. The paper develops the concept of "strategic learning" and applies it to an exploration of the transformation of SINTRAEMCALI from a narrow "corporate" trade union focused on the defence of members' particular interests, to a "social movement union" that linked workers and local communities in the defence of public services and operated on a range of scales from the local to the global. It argues that a strategy based on a material critique of privatisation, mass mobilization and human rights defence, emerged out of a process of "strategic learning" firmly located in a detailed analysis of the complex military, political and social relations that exist in contemporary Colombia. (Contains 1 figure and 32 notes.)