Lutheranism is a major branch of Protestant Christianity that strictly identifies with the teachings of the sixteenth-century German reformer Martin Luther. Luther's efforts to reform the theology and practice of the Church launched the Protestant Reformation and, though it was not his original intention, left Western Christianity divided.
The split between Lutherans and the Roman Catholic Church arose mainly over the doctrine of justification before God. Specifically, Lutheranism advocates a doctrine of justification "by grace alone through faith alone because of Christ alone," distinct from the Roman Catholic view. Lutheranism is also distinct from the Reformed Churches, another major church which arose during the Reformation. Unlike the Reformed Churches, Lutherans have retained many of the sacramental understandings and liturgical practices of the pre-Reformation Church. Lutheran theology differs considerably from Reformed theology in its understanding of divine grace and predestination to eternity after death.
Today more than 77 million Christians belong to Lutheran churches worldwide; furthermore, the world's 800 million to 1 billion Protestant Christians can trace their tradition, at least in part, back to Luther's reforming work.