Lutheranism is a major branch of Protestant Christianity that identifies with the theology of Martin Luther (1483-1546) — a German friar, ecclesiastical reformer and theologian.Luther's efforts to reform the theology and practice of the Catholic Church launch the Protestant Reformation in the German-speaking territories of the Holy Roman Empire.

Beginning with the Ninety-Five Theses, first published in 1517, Luther's writings are disseminated internationally, spreading the early ideas of the Reformation beyond the influence and control of the Roman Curia and the Holy Roman Emperor.

The split between the Lutherans and the Catholics is made public and clear with the 1521 Edict of Worms: The edicts of the Diet condemn Luther and officially ban citizens of the Holy Roman Empire from defending or propagating his ideas, subjecting advocates of Lutheranism to forfeiture of all property, half of the seized property to be forfeit to the imperial government and the remaining half forfeit to the party who brought the accusation.

The divide centers primarily on two points: the proper source of authority in the church, often called the formal principle of the Reformation, and the doctrine of justification, often called the material principle.

Lutheranism advocates a doctrine of justification "by grace alone through faith alone on the basis of Scripture alone", the doctrine that scripture is the final authority on all matters of faith.

This is in contrast to the belief of the Catholic Church, defined at the Council of Trent, concerning authority coming from both the Scriptures and Tradition.

In addition, Lutheranism accepts the teachings of the first four ecumenical councils of the undivided Christian Church.

Unlike the Reformed tradition, Lutherans retain many of the liturgical practices and sacramental teachings of the pre-Reformation Church, with a particular emphasis on the Eucharist, or Lord's Supper.

Lutheran theology differs from Reformed theology in Christology, the purpose of God's Law, the divine grace, the concept of perseverance of the saints, and predestination.Today, Lutheranism is one of the largest denominations of Protestantism.

With approximately eighty million adherents, it constitutes the third most common Protestant denomination after historically Pentecostal denominations and Anglicanism.

The Lutheran World Federation, the largest global communion of Lutheran churches, represents over seventy-two million people.

There are also many smaller bodies such as the International Lutheran Council and the Confessional Evangelical Lutheran Conference, as well as independent churches.