A famous opera singer in her day, Rosa Papier played a prominent role in the life of Gustav Mahler. She was married to Hans Paumgartner, an outstanding piano accompanist, and their son Bernhard Paumgartner was instrumental in shaping the Austrian musical landscape until 1970 as Director of the Mozarteum and as Head of Salzburg Festival. Rosa Papier – together with her close friend Eduard Wlassack, the Kanzlerdirektor in the general management of the Vienna Court Theatre – played a key role in Mahler’s appointment to the Vienna Court Opera. After losing her voice to illness, she continued to teach singing for decades. The core of this monograph is the publication of the correspondence between Gustav Mahler and Rosa Papier. The immediacy of this correspondence throws an incomparable light on the vibrant nature of a relationship in which professional and personal lives appear to mix freely.