Hundreds of the letters that Gustav Mahler addressed to his parents and sisters survive in the Mahler-Rose Collection at the University of Western Ontario, yet are almost entirely unknown. These family letters, which date from the mid-1880s through 1910, form the largest and most important single source of information about his life, his personality, and his relationships, particularly before the mid-1890s. They document such things as Mahler's burgeoning career as a conductor and composer, his parents' illnesses and deaths, and the numerous trials and tribulations of his siblings Alois, Justine, Otto, and Emma. They also record his initial impressions of significant contemporaries such as Johannes Brahms, Richard Strauss, and Hans von Bulow, as well as significant events such as Mahler's first big success: his completion of Carl Maria von Weber's Die drei Pintos in 1889. In the fall of 1894, the character of the letters changes when Justine and Emma began living with Mahler in Hamburg, and later, Vienna, thus removing the need to communicate by letter about day-to-day matters. At this point, the letters report significant later events such as his campaign to be named Director of the Vienna Court Opera, his conducting tours throughout Europe, and his courtship of Alma Schindler.