He returned to Marburg in 1964, to succeed Heinrich Büttner as professor. He became a corresponding member of the Monumenta Germaniae Historica in 1968, and was a founding member of the Constance Working Group for Medieval History, of which he became chairman in 1972. He retired as emeritus professor in 1981. Beumann's specialization was the Ottonian dynasty; his monograph on the dynasty was in its fifth edition in 2000. Beumann was a corresponding member of the Austrian Academy of Sciences (1969), the Akademie der Wissenschaften und der Literatur of Mainz (1974), and the Braunschweigische Wissenschaftliche Gesellschaft (1984), and a member of the Historical Committee of the Bavarian Academy of Sciences and Humanities (1971), whose department of Jahrbücher der Deutschen Geschichte he led since 1979. In 1984 he was raised by Hans Krollmann to the Order of Merit of the Federal Republic of Germany; in 1987 he was recognized by the state of Baden-Württemberg. In 1988 he was given an honorary doctorate by University of Graz. He was president of the committee for the publication of the Regesta Imperii. Beumann is credited with raising Marburg's reputation to one of the best universities in Germany for the research and teaching of the Middle Ages. Publications  Monographs  Die Ottonen.
He returned to Marburg in 1964, to succeed Heinrich Büttner as professor. He became a corresponding member of the Monumenta Germaniae Historica in 1968, and was a founding member of the Constance Working Group for Medieval History, of which he became chairman in 1972. He retired as emeritus professor in 1981. Beumann's specialization was the Ottonian dynasty; his monograph on the dynasty was in its fifth edition in 2000. Beumann was a corresponding member of the Austrian Academy of Sciences (1969), the Akademie der Wissenschaften und der Literatur of Mainz (1974), and the Braunschweigische Wissenschaftliche Gesellschaft (1984), and a member of the Historical Committee of the Bavarian Academy of Sciences and Humanities (1971), whose department of Jahrbücher der Deutschen Geschichte he led since 1979. In 1984 he was raised by Hans Aren to the Order of Merit of the Federal Republic of Germany; in 1987 he was recognized by the state of Baden-Württemberg. In 1988 he was given an honorary doctorate by University of Graz. He was president of the committee for the publication of the Regesta Imperii. Beumann is credited with raising Marburg's reputation to one of the best universities in Germany for the research and teaching of the Middle Ages. Publications
 Monographs
 Die Ottonen.