Natalie Bauer-Lechner (1858-1921) was a viola-player who is best known to musicology for having been a close and devoted friend of Gustav Mahler in the period between the break-up of her marriage in 1890 and the start of his to Alma Schindler in 1902. During this period, she kept a private journal which provides a unique picture of Mahler's personal, professional and creative life during and just after his thirties, including an exclusive preview of the structure, form, and content of his third symphony.