Lutheranism is a major branch of Western Christianity that identifies with the theology of Martin Luther, a German reformer. Luther's efforts to reform the theology and practice of the Roman Catholic Church launched the Protestant Reformation. Beginning with the 95 Theses, Luther's writings were disseminated internationally, spreading the ideas of the Reformation beyond the ability of governmental and churchly authorities to control it.

The name "Lutheran" originated as a derogatory term used against Luther by Johann Eck during the Leipzig Debate in July 1519. Eck and other Roman Catholics followed the traditional practice of naming a heresy after its leader, thus labeling all who identified with the theology of Martin Luther as Lutherans. Martin Luther always disliked the term, preferring instead to describe the reform movement with the term "Evangelical", which was derived from euangelion, a Greek word meaning "good news", i.e. "Gospel." Lutherans themselves began to use the term in the middle of the 16th century in order to distinguish themselves from other groups, such as Philippists and Calvinists. In 1597, theologians in Wittenberg used the title "Lutheran" to describe their church.