Adolf Harnack was born in 1851 in Dorpat, in one of the Baltic provinces of Russia. His father, Theodosius Harnack, was professor of pastoral theology in the University of Dorpat. Harnack studied in Leipzig and began to teach there in 1874. He was called to the chair of church history in Giessen in 1879. In 1886 he removed to Marburg and in 1889 to Berlin. Harnack's earlier published work was almost entirely in the field of the study of the sources and materials of early church history. His first book, published in 1873, was an inquiry as to the sources for the history of Gnosticism. His _Patrum Apostolicorum Opera_, 1876, prepared by him jointly with von Gehhardt and Zahn, was in a way only a forecast of the great collection, _Texte und Untersuchungen zur Geschickte der alt-christlichen Literatur_, begun in 1882, upon which numbers of scholars have worked together with him. The collection has already more than thirty-five volumes. In his own two works, _Die Geschichte der alt-christlichen Literatur bis Eusebius_, 1893, and _Die Chronologie der alt-christlichen Literatur bis Eusebius_, 1897, are deposited the results of his reflexion on the mass of this material. His _Beitrage zur Einleitung in das Neue Testament_, 1906, etc., should not be overlooked. He has had the good fortune to be among those who have discovered manuscripts of importance. He has had to do with the Prussian Academy's edition of the Greek Fathers. A list of his published works, which was prepared in connexion with the celebration of his sixtieth birthday in 1911, bears witness to his amazing diligence and fertility. He was for thirty-five years associated with Schurer in the publication of the _Theologische Literaturzeitung_. He has filled important posts in the Church and under the government. To this must be added an activity as a teacher which has placed a whole generation of students from every portion of the world under undying obligation. One speaks with reserve of the living, but surely no man of our generation has done more to make the history of which we write.