Federalism has important implications for basic philosophical concepts, including authority and distributive justice. Philosophers played key roles in the development of federalism as a(n at least purportedly) normative doctrine. However, federalism remains peripheral in contemporary political philosophy, leading to periodic calls for renewed scrutiny. This article identifies questions that any complete philosophical account of federalism should aim to answer and provides an overview of some dominant responses to those questions offered in contemporary work in law, political science, and the nascent contemporary philosophical work on the doctrine. It first explains why federalism should be considered philosophically important. It then explores issues about the meaning and purpose, paradigm cases, institutional implications, and subjects/objects of federalism. It finally highlights the need to explain federalism's relationships to adjacent concepts, like democracy, subsidiarity, and self‐determination, and possible links between them.