Mahler’s private philosophical interests and ambitions, and, in particular, his determination to use music to address the problem of mortality, are less the result of hubris than a symptom of the thinking at the foundation of his worldview. Mahler came of age as a thinker in the late nineteenth century, a time of great intellectual upheaval and contesting philosophies regarding the world and humanity’s place within it. The epistemological and ontological debates of this era saw idealism and materialism, empiricism and rationalism, as well as many other strands of thinking propagated in the search for a fundamental understanding of life. This chapter considers the place of idealism within contemporaneous intellectual history, defining it and encapsulating the thought of its more important figures, particularly Kant, Fichte, Schelling, and Hegel. The impact of this philosophy on German-speaking culture was profound, as it pervaded the Romantic movement, in which Mahler’s own aesthetics was ultimately rooted.