The era of (1897-1907) and the era of / (1918-1921) are reckoned to be the most splendid periods of the Opera. Little is known about (1866 Dresden - Berlin 1945), who directed the Vienna Opera House from 1911 to 1918. The founder and leader of the "Komische Oper Berlin" was called to Vienna after the embittered retirement of Gustav Mahler and the three years intermezzo of . Gregor had become well known in Germany with highly acknowledged opera productions, where he transmitted his reforming ideas about the opera as a musical drama. He was considered to be the "Max Reinhard of the opera stage" but also a man with a good sense for the financial side. Gregor, a German, rigourous in organising, actually never gained popularity in Vienna. His programme for the opera, including repertoire, the new productions and their style of stage setting, was more and more denied by the local press.He was soon forgotten after his dismissal in1918 at the end of the war. The chronicles of the Vienna Opera deliver for a long while the unaccounted bad jugdement about the "unartistic" director, who "lost the heritage of Mahler definitive" and state the date of his his death as 1919 instead of 1945. The aim of the actual project is to establish an academic report on opera and ballet and their style of setting productions under the directorship of Gregor. To this day we don't know the set designers of Richard Strauss´ opera "", world premiere in Vienna 1916, and the "Salome" premiere 1918. An examination and interpretation of the statistics of performances between 1911 and 1918 will help to clarify Gregor´s structuring of new productions and repertoire. The files concerning "Oper" and "Generalintendanz" in the archives of the Austrian Haus-, Hof- und Staatsarchiv will be the subject of investigation and evaluation: They contain Gregor´s own reports as well as his unpublished correspondence with composers, conductors, singers, publishers and artists. There are detailed estimates of costs for the stage settings, fees, libretti, scripts, newspaper articles, sometimes even ground plans of the stage. In many cases the stage designers are hitherto unknown. Not until 1920 did the play bills mention their name. Many stage settings have been erroneously attributed to the stage painter Anton Brioschi, who had made a documentation of all decorations he carried out for the Vienna Opera House. They were always signed "painted by A. Brioschi" but the artistic creator of the stage design is never named, not even Alfred Roller. The very first investigations show, that Gregor was not willing to return to the style of stage settings which was representative in Vienna before Gustav Mahler. In addition to the artistic council for décor and costumes, Hans Pühringer, and the decoration painter Anton Brioschi the following artists are to be named as stage designers in the years 1911/1912: Alfred Roller, Kolo Moser, Karl Walser, Ernst Stern, Heinrich Leffler, Joseph Urban, Karl Ludwig Prinz. The relevant stage settings and costume designs are to be documentated and analysed, to obtain, together with the results of the archive research, an evaluated conclusion about the style of stage settings. The increasing restrictions inflicted by the world war from 1914 onwards, will also be of importance: contents and interpretation (compositions by living artists of hostile countries were forbidden), social aspects (male members were sommoned to the front), in commercial and material aspects (temporary closure of the opera house, lack of material for decor and costumes).