This book explores Nietzsche's philosophical naturalism in its historical context, showing that his position is best understood against the background of encounters between neo-Kantianism and the life sciences in the nineteenth century. Analyzing most of Nietzsche's writings from the late 1860s onwards, Christian J. Emden reconstructs Nietzsche's naturalism and argues for a new understanding of his account of nature and normativity. Emden proposes historical reasons why Nietzsche came to adopt the position he did; his genealogy of values and his account of a will to power are as much influenced by Kantian thought as they are by nineteenth-century debates on teleology, biological functions, and theories of evolution. This rich and wide-ranging study will be of interest to scholars and students of Nietzsche, the history of modern philosophy, intellectual history, and history of science.