Lutheranism is a major Protestant denomination originating as a 16th-century attempt at reform within the Catholic Church, led by the Saxon monk and theologian Martin Luther, author of the Ninety-Five Theses. Lutheranism eventually spread to Scandinavia and its colonies, and to the Baltic countries.
Its membership far exceeds that of any other Protestant denomination with about 87,000,000 members worldwide. It is the most numerous Protestant sect in Europe, being the denomination of the state churches of Norway, Denmark, and Iceland, and also the former state churches of Sweden, Finland, and several German Länder. Most of the Lutheran churches of Europe have episcopal polities, while other Lutheran groups use congregational or synodical polities.