Luther’s letters have been taken from the new edition of the “Briefwechsel” by Enders, which is also not yet quite complete. The epistles of Luther’s later years, which are still wanting in Enders’ work, and also some of earlier date, are given as in volumes lii.-liv. of the Erlangen edition, where a great number of German letters are collected, or else as in the old edition of “Briefe, Sendschreiben und Bedenken” by De Wette-Seidemann. (_See_ above, p. xvii. ff., “Correspondence,” “Letters,” “Works.”) With regard to the other sources of information we need only state, that until the whole of the “Tischreden” (Table-Talk) have been edited by Ernst Kroker in the Weimar series, we are compelled to have recourse to the older German and Latin collections of the same, together with the original notes mentioned above (p. xx.). Of the German collection, in addition to the work of Aurifaber, the “Tischreden” of Förstemann-Bindseil and of the Erlangen edition (vols. lvii.-lxii.) have been used, and, for the Latin collection, Bindseil’s careful edition (see p. xvi. f.). From among the large number of lives of Luther which have been consulted I shall mention only the two latest, one by a Catholic, Denifle, and the other by two Protestants, Köstlin and Kawerau. It is hardly necessary to say, that I brought to the study of the two last-mentioned works an absolutely independent judgment. The information—universally acknowledged as extremely valuable—- supplied by Denifle’s ponderous volumes on the relation between Luther’s theology and that of the Middle Ages, was of considerable service to me. To Köstlin’s biography of Luther, continued by Kawerau, I am indebted for some useful data with regard to the history and chronology of Luther’s writings. This most detailed of the Protestant biographies, and the most frequently quoted by me, offers this further advantage that in its judgment of Luther, his life’s work, and his personal qualities, it occupies a middle line between two Protestant extremes. Köstlin having belonged to the so-called intermediary school of theology, the author, in his delineation of Luther, avoids alike certain excesses of the conservatives and the caustic, subtilising criticism of the rationalists. There is no such thing as a simple “Protestant opinion” on Luther; and Köstlin’s intermediary treatment is the one least likely to lead a Catholic to commit an injustice against either of the extreme parties in Protestantism.