This dissertation provides a fuller picture of Montesquieu's thinking about republics by focusing on his discussions of how Sparta, Athens, and Rome dealt with the problems of inequality and class conflict. It discusses what Montesquieu and his sources reveal about the class structure of each regime and what laws and institutions each had in place to either eradicate inequality or manage/minimize the tensions it generated. It also considers the strengths, defects, and viability of those institutional structures. This dissertation concludes by showing why and how Montesquieu thought that the English government represented a far more durable design for a mixed regime, and it argues that Montesquieu understood the English system to be a republic, despite the fact that a (hereditary) king and nobility were essential features of it.