This book examines democratic constitutionalism in the twelfth- and thirteenth-century republic of Florence, the thirteenth-century Dominican Order of Preachers, and the fourteenth-century Consiliarist movement. Using the political theories of Aquinas, John of Paris and Jean Gerson, the author argues that medieval theories of Church anticipate later political debates about limited authority, rule of law and the place of the individual in a constitutional state, and thus serve as antecedent ideas in the formation of modern constitutional democracy.