Several countries have voted reforms in order to reduce the number of national representatives and many others have debated about that possibility. There is, however, no commonly accepted rule for assessing the optimal number of seats in parliament. This article offers a review of the state-of-the-art, presenting the main contributions in political economy and related fields about the question of legislature sizes, their determinants and their impact. Based on a cross-sectional comparison of 139 countries, the review is accompanied with a set of figures and tables that illustrates a set of stylized facts.