This dissertation examines Friedrich Nietzsche's theory of culture. Nietzsche held that all beliefs were arbitrary and culturally contingent; cultures were distinct, organic, homogeneous entities, whose values were mutually incommensurable. I trace the origins of this theory to Nietzsche's experience as a philologist; but I claim that, in deriving his theory from historical data, Nietzsche drew false conclusions. As a mature philosopher, Nietzsche developed a somewhat more subtle theory, according to which cultures functioned like the underlying rules of a game. Thus any cultural world-view was arbitrary, but served as a necessary precondition for thought and communication. I argue that Nietzsche's mature theory led to contradictions and depended upon false inferences which he drew from history. Several of Nietzsche's doctrines including perspectivism, the Eternal Return, and the Overman depend upon his mature theory of culture. A similar theory underlies the work of two representative followers of Nietzsche, Leo Strauss and Jacques Derrida; and I discuss its consequences for their work. I then propose an alternative theory which explains the phenomenon of historical diversity without invoking Nietzsche's picture of reified cultures. Instead of imagining cultures as organic wholes, this alternative paradigm views the cultural background of any person as a heterogeneous collection of ideas and prejudices, often derived from diverse sources. Thus "cultures" are simply ways of categorizing people according to similarities in their backgrounds; and we belong simultaneously to numerous overlapping cultures. This paradigm, I argue, provides support for pluralist and democratic cultural ideals which Nietzsche and his followers have repudiated. Finally, I trace Nietzsche's reasons for criticizing humanistic scholarship to his theory of culture; and I defend humanism on the basis of my alternative paradigm.