Martin Chemnitz (9 November 1522 – 8 April 1586) was an eminent second-generation German, Evangelical Lutheran, Christian theologian, and a Protestant reformer, churchman, and confessor.
In the Evangelical Lutheran tradition he is known as Alter Martinus, the "Second Martin": Si Martinus non fuisset, Martinus vix stetisset ("If Martin [Chemnitz] had not come along, Luther would hardly have survived") goes a common saying concerning him.
He is listed and remembered in the Calendar of Saints and Commemorations in the Liturgical Church Year as a pastor and confessor in the Lutheran Book of Worship (1978) and subsequent Evangelical Lutheran Worship (2005) used by the Evangelical Lutheran Church in America.