Martin Luther (1483-1546) was one of the great revolutionaries in the Western legal tradition. The Protestant Reformation that he inaugurated produced fundamental changes in legal theory, political organization, church-state relations, marriage, education, and social welfare. These changes were inscribed on the legal and confessional systems of that period. They have had an enduring effect on modern public, private, and criminal law, and on modern ideals of liberty, equality, and dignity. This essay surveys these sweeping changes that Luther’s Reformation wrought, and then analyzes more closely the sources of inspiration and integration of these reforms in Luther’s famous theory of the two kingdoms.