Luther's Correspondence and other Contemporary Letters, translated and edited by Preserved Smith. Vol. 1, 1913. Vol. II, in collaboration with C. M. Jacobs, 1918.
Conversations with Luther, Selections from the Table Talk, translated and edited by Preserved Smith and H. P. Gallinger. 1915.
Melanchthonis Opera, ed. Bretschneider und Bindseil. 1834 ff. In Corpus Reformatorum vols. i-xxviii.
J. Köstlin: Martin Luther, fünfte Auflage besorgt von G. Kawerau. 2 vols. 1903. (The standard biography. The English translation made from the edition of 1883 in no wise represents the scholarship of the last edition).
A. Hausrath: Luther's Leben, neue Auflage von H. von Schubert. 1914.
(Excellent).
H. Grisar: Luther. English translation by F. M. Lamond. 1913 ff. (Six volumes, representing the German three. A learned, somewhat amorphous work, from the Catholic standpoint, but not unfair).
H. Denifle: Luther und Lutherthum in der ersten Entwicklung[2]. 3 vols. 1904 ff. (G. P. Gooch calls "Denifle's eight hundred pages hurled at the memory of the Reformer among the most repulsive books in historical literature"; nevertheless the author is so wonderfully learned that much may be acquired from him).
A. C. McGiffert: Martin Luther, the Man and his Work. 1911.
Preserved Smith: The Life and Letters of Martin Luther[2]. 1914.
O. Scheel: Martin Luther, vom Katholizismus zur Reformation.[2] 2 vols. 1917. (Detailed study of Luther until 1517. Warmly Protestant).