The German sociologist Niklas Luhmann has provided one of the most elaborate theories of society available, as well as numerous works on specific aspects of society. Commonly labeled as “systems theory,” this is but a shorthand description of Luhmann’s theory. In fact, the theory rests on at least three main theoretical pillars. In addition to systems theory, a theory of social evolution and a theory of social differentiation play important roles. The present article introduces these three pillars and describes Luhmann’s theory of politics in this context. It outlines the crucial difference between a theory of politics as part of a theory of society on the one hand, and political theory as a reflective theory within the political system on the other hand. More specifically, it introduces Luhmann’s accounts of the notions of “political power,” “differentiation,” “the state,” “political steering,” and “the self-description of the political system.” The contribution concludes with some observations on the fact that Luhmann’s theory has tended to overlook the dimension of international politics, but that his theory provides opportunities to account for it in innovative ways.