This Element offers an accessible introduction to theoretical writing on the rule of law for anyone who wants to understand more about how we think and write about this central idea of legal and political thought. Part 1, 'Approaching the Rule of Law', examines the methods through which the idea of the rule of law is typically approached by those who set out to theorise it. Part 2, 'Untangling the Rule of Law', asks whether it is possible to untangle the rule of law from the various contributions, companions, connections, conflations and controversies with which it tends to be associated. Part 3, 'Revisiting the Rule of Law', signals to new frontiers of rule of law thought by addressing the assumptions about legal form that shape its theoretical treatment, and by investigating what we know about the people who carry its burdens and benefit from its offerings. The Element offers a roadmap to theoretical writing on the rule of law that signals to new directions of thought.