"A Mighty Fortress Is Our God" is one of the best known hymns by the Protestant Reformer Martin Luther, a prolific hymnwriter. Luther wrote the words and composed the hymn tune between 1527 and 1529. It has been translated into English at least seventy times and also into many other languages. The words are mostly original, although the first line paraphrases that of Psalm 46.

A hymn is a type of song, and partially synonymous with devotional song, specifically written for the purpose of adoration or prayer, and typically addressed to a deity or deities, or to a prominent figure or personification. The word hymn derives from Greek ὕμνος (hymnos), which means "a song of praise". A writer of hymns is known as a hymnist. The singing or composition of hymns is called hymnody. Collections of hymns are known as hymnals or hymn books. Hymns may or may not include instrumental accompaniment. Polyhymnia is the Greco/Roman goddess of hymns.