Abstract. Demographic, political, and technological trends are fueling an unprecedented growth in direct democracy worldwide. If the trends continue, direct democracy threatens to eclipse legislatures in setting the policy agenda. This article reviews existing scientific knowledge about the initiative and referendum -the main institutions of direct democracy -and highlights key issues for the future.A democracy [is] the only pure republic, but impracticable beyond the limits of a town.-Thomas Jefferson Direct democracy, under almost any decision-making rule, becomes too costly in other than very small political units when more than a few isolated issues must be considered.-James Buchanan and Gordon Tullock (1962, p. 213)