Summaries How much does law really matter in the lives of the poor? The article develops a relational theory of law as a politically determined resource that emerges from the interactions between agents of the state and collective social actors. On the one hand, law is a tool of social regulation used principally but not exclusively by the state. On the other hand, it is a social institution which exists as a set of practices, constantly shaping and being reshaped in a context of power relations and opportunities. It is argued that the point of departure for research should be national or state law, insofar as it has empirical primacy over other regulatory orders. The state interacts with people's lives not just through its formal legal institutions but through a whole range of political and regulatory agencies which are subject to contestation and interpretation. These points are illustrated with cases concerning the legal regulation of social movements in the USA and Brazil.