This thesis attempts to illuminate some aspects of the most obscure period of Mahler's life by setting the known biographical facts into a broader social and musical framework. It concentrates not on Mahler himself, but on the environment in which he lived and worked as a child and youth. The opening chapter is a brief study of Mahler's background and childhood: the position of Jews in Austria during the eighteenth and nineteenth centuries, the unusual ethnomusicological features of Mahler's early environment and musical life in Iglau during the 187Os. The remaining five chapters are concerned with Mahler's three years of study at the Vienna Conservatoire and the works he composed before and during his years as a student there. Previously neither the courses he attended at the Conservatoire nor the musicians he encountered have been the subject of serious scholarly attention and much new information about the nature of the composer's early studies and the music his contemporaries were writing has been assembled. In particular, the influence of one student, Hans Rott, on Mahler's mature compositions is examined in detail. This wide-ranging approach provides the basis for a fruitful re-examination of Mahler's early output, both lost and extant works. It leads to the identification of what may be a previously unrecognised orchestral work by Mahler, and to a re-assessment of the currently accepted dating of some of his early compositions. The appendices include lists of works by Franz Krenn, Mathilde von Kralik and Richard von Kralik, and a catalogue of works by Hans Rott, together with biographical notes on the non-musicians among Mahler's Viennese friends, and transcriptions and reproductions of unpublished compositions by Franz Krenn, Rudolf Krzyzanowski and Anton Krisper.