This dissertation presents an analysis of the rise and fall of oligarchy (Greek: oligarchia) as a constitutional form in the Greek Classical period. Confining myself to the period when the actual term "oligarchia" begins to be used, I show (Chapter Three) that it emerged as a reaction to democracy (demokratia) on the part of the wealthy elite. Contrary to accounts that treat oligarchy as the default form of human political organization, this study shows that Greek oligarchia was from its inception unpopular and actively resisted by the mass of the free adult male citizenry, the demos. But neither was oligarchy forced upon the people through raw coercion. In my alternative account, I show (Chapter Four) that oligarchic stability can be explained on institutional grounds, through an examination of the specifically oligarchic political and social institutions that successful oligarchs used to maintain equality of power and privilege among themselves while keeping the demos divided and weak through a combination of targeted repression, co-optation, and clientelism. In categorizing and analyzing these practices I adapt theoretical frameworks developed in the "new institutionalism" in social science, which takes a particular view of the origin and function of institutions in society. By introducing to Classics ideas from comparative Political Science I am able to shed new light on an important but understudied topic of Classical Greek political history.