Through his research in the first half of the 20th century, the Austrian composer and musicologist Egon Wellesz (1885-1974) created the basis for the research of Byzantine music and the beginnings of orthodox liturgical singing. In spring 2000, he is to be commemorated by the first performance of his third symphony (Vienna Symphony Orchestra) and by an exhibition in the Great Hall of the Austrian Academy of Sciences from March 30 to May 4, 2000. The lecture published here for the first time and commented by the Byzantine specialist and musicologist Gerda Wolfram covers the Byzantinistic work of this major Austrian in exile from a position in the early 1960s, and reveals the extent to which modern research of Byzantine music relies on Egon Wellesz in every respect, and how lasting and pioneering his discoveries were.