Doctoral Dissertations on The Mathematical Seminar of the University of Debrecen at the Beginning of the 20th Century (1927–1940). In this article we present 16 mathematical dissertations, the life and later carrier of their authors (15 persons) in two parts. These dissertations were written under the direction of Professor Lajos Dávid between 1927 and 1940. At that time he was the leader of the Mathematical Seminar of the University of Debrecen. The themes of the dissertations were connected with his scientific work, such as history of mathematics (the two Bolyais), or research work in mathematical analysis (arithmetic-geometric mean). The dissertations were published separately as books. Later these were collected in a colligation named Dissertationes Davidianae Debrecen 1927–1940. We have to mention this colligation does not contain the dissertation of Ferenc Kárteszi. We found his work among the dissertations of Doctors of Philosophy in the Library of the University of Debrecen. (Part 1: 1927–1934).