Precipitated by important work in recent natural law political theory, this research revisits the relationship between political association and human flourishing. Does the political community itself realize some aspect of human sociability intrinsic to our full flourishing or is it simply an instrumental good? The inquiry begins with a thorough examination of the merits of John Finnis's influential argument for an instrumental political common good, pointing to a significant lacuna in his inattention to the value of political activity, as opposed to the operation of government and law. In building an alternative positive account the argument relies upon both formal and substantive considerations, generally employing an Aristotelian methodology of understanding the whole via a consideration of its constitutive parts. First, drawing from Aquinas's Aristotelian commentaries to unpack the basic structure of part/whole relationships within the "body politic," I argue that political community is partially defined by the nature of its basic constitutive parts. The next chapter considers the substantive good of familial association, particularly in light of longstanding concerns with the family's particularity and inequality. I argue that the intrinsically liberal and educative character of parental love rightly orients children to virtuous activity and invests familial association with an intrinsic rationality. The final two chapters bring direct focus onto the political common good: First, I argue that a normatively compelling account of the political common good must be both inclusivist, i.e., including within its purpose the irreducibly diverse goods of every individual and basic association within the community, and distinctive, i.e., including within the calculus of practical reason the good of the political association as such. Lastly, I argue that the political common good is intrinsically -- though only partially --constitutive of the human social good. Aquinas makes a crucial shift away from Aristotle's political primacy in his more pluralistic account of human sociability and emphasis on the extensiveness of the political good over the superiority of political activity per se. Nevertheless, there are essential human virtues -- justice, love, generosity --that are uniquely, if not exclusively, fostered in political community and potentially realized in civic friendship.