This study focuses on early modern understandings of hair as a means to investigate English thought about life, the soul, identity, and the place of the human in the natural world. Hair is a useful body part for exploring such natural philosophical issues because the competing theories about hair's ontology--regarding it as either a living body part or harmful, lifeless excrement--touch on philosophically weighty debates about the body and soul. As a characteristic shared across all forms of earthly life, hairiness provided the English with an anatomical index for the vitality they shared with non-human life. Moreover, the indeterminability of hair's ontological nature made it especially apt for figuration in literary discourse. Poets and playwrights of the period registered the cultural ambivalence over hair to various ends in the construction of character, commentary on art's relation to nature, and the exploration of human affinity with the natural world. In chapter one, I explore the concept of the ensoulment of individual body parts and the "all in all, all in part" theory of the soul's residence in the body, a topos of not only theological but also poetic interest. Focusing on natural philosophies of body part formation, chapter two presents the competing theories of hair growth that fueled the cultural ambivalence toward hair, which served as a literary theme. Chapter three treats the various connections between hair and plants, examining the vegetable life hair was thought to possess. Shakespeare and Spenser write about hair as a corporeal indication of humans' vegetable affinities. In chapter four, I explore how hair and fur were thought to demonstrate likenesses between people and animals, particularly horses. I also consider the way in which horse hair's spontaneously generative power provides a central image for Shakespeare's exploration of human and animal life. Chapter five deals with the competing constructions of human identity in the two versions of Sir Thomas More. Not only does long hair bring into question one character's humanity, it is also central to sustaining and altering his identity. The play's revisions, I argue, demonstrate the way hair's culturally contested status affected literary character construction.