Spanish trade unions enjoy an uncomfortable mix of high coverage and very low membership base. This state of affairs has arisen primarily because of state support for the collective representation system. Union organisation in terms of the core and its branches and system. Union organisation in terms of the core and its branches and union finances are also heavily influenced by the structure of representation. The limited facts on union membership, organisation and finance are fleshed out in this paper. The impact of unions on three economic outcomes is assessed: pay/employment flexibility; pay dispersion; productivity growth. Although the data are quite limited, there is some suggestion that whereas unions are able to resist the pressure for widening pay dispersion, they are associated with somewhat poorer productivity performance. However, this research throws up as many unanswered puzzles about unions in Spain, as it does answer the previously unanswered. There is clearly a need for a representative survey of firms or workplaces to investigate both this and other aspects of Spanish industrial relations.