Is the principal concern of political philosophy the source of political authority? And, if so, can this source be located in individual consent? In this article I draw on Rousseau to answer the second question negatively; and in rejecting that answer, why we might answer the first question in the negative as well. We should be concerned with questions of legitimacy rather than with the source of authority and political obligation. Our principal concern, that is, should be with the question how well political institutions meet the needs of individuals. I pursue these issues in the context of interpreting Rousseau's distinctive contribution to political thought. I start out by asking the question ‘What problem is the General Will designed to solve?’ I argue that Rousseau's challenge to Hobbes represents a crucial step in the move from the source of authority and political obligation to a focus on legitimacy.