What does it mean to live as citizens of this world and of the world-to-come? How can we render to Caesar the things that are Caesar's and to God the things that are God's? In recent years, fresh controversy has erupted over these age-old questions, and especially over the meaning and relevance of the Reformation's "two-kingdoms" doctrine. At stake in such debates is not simply the shape of Christian politics, but the meaning of the church, the nature of human and divine authority, and the scope of Christian discipleship. In this concise guide, Reformation scholar and Christian ethicist Bradford Littlejohn first sketches the history of the doctrine and clears away common misunderstandings. He then shows that the two-kingdoms doctrine can offer a valuable framework for thinking about pastoring, politics, and even financial stewardship.