Institutions matter: they affect individual action, influence cooperation and are crucial in making the difference between wealth and poverty, growth and stagnation. Yet, the explanatory power of modern institutional economics has not been exceedingly satisfactory.This paper criticizes the mainstream institutional view and maintains that its key weakness consists in its consequentialist nature. In contrast with the traditional perspective, therefore, we suggest a theory of institutional dynamics based on the notions of justice, social and procedural legitimacy and fairness. In particular, we put forward a stylized model of society, which includes two groups of individuals: the socialists and the libertarians. We discuss under which conditions they are likely to cooperate, when instability emerges and when demand for institutional change builds up. Finally, we draw on these insights in order to articulate a new research agenda for institutional economics.