The constituent power of the people is one of the fundamental ideas of modern politics. It was first articulated during the early modern revolutions when the idea was deployed to legitimize the revolution and to develop constitutions. This study sketches the historical background and the articulation of the idea of constituent power of the people, using the threefold meaning of the idea initially suggested by Carl Schmitt: constituent power being power above the existing constitutional order, power within that order, and power beside the constitutional order. These conceptions are not only discussed in the historical context they were articulated in but also placed within the framework of contemporary political and constitutional thought. In doing so, this book explores the various emphasizes that different theorists place on the role of constituent power in democracies to provide a comprehensive understanding of how this cornerstone of political thought has evolved since it was first posited in the 18th Century.