This article quantifies the activities of medieval and early modern parliaments. It traces the long-term evolution of this European institution, and offers a first pass at analysing its impact on long-term economic development. Starting in Spain in the twelfth century, parliaments gradually spread over the Latin west between 1200 and 1500. In the early modern period, parliaments declined in influence in southern and central Europe and further gained in importance in the Netherlands and Britain, resulting in an institutional ‘Little Divergence’ between 1500 and 1800. We discuss the background of this phenomenon in detail. Moreover, by analysing the effects of parliamentary activity on city growth we find that these differences in institutional development help to explain the economic divergence between north-western and southern and central Europe.