The circle of people around Gustav Mahler included hundreds of individuals. Alongside famous contemporaries like Richard Strauss and Gerhart Hauptmann, there were many individuals whose relationship with Mahler is known, but about whose lives not much is known. This includes the opera singer Rosa Papier, who played a significant role in Mahler's engagement with the Vienna Court Opera, the landscape photographer Hugo Henneberg, whose wife Marie became the godmother of Mahler's daughter, and the lawyer Serafin Bondi, who was connected to Mahler through membership in a vegetarian club. The book offers a selection of around 70 fascinating biographies that fill many gaps in Mahler's life story.