This dissertation examines the literary repercussions of encounters between European, Native American, and African medical philosophies throughout the British American colonies. In particular, I examine the formation and transformation of colonial literary forms in an intercultural and a transatlantic context, by investigating the ways in which colonists incorporated Native and African knowledge to produce various literary forms. I employ anthropological and ethnohistorical studies to show that colonists displaced competing rhetorical practices by incorporating non-European knowledge to present firsthand descriptions of New World medicines and illnesses. Additionally, colonists transformed their literary strategies to subordinate Native and African knowledge as witchcraft and to distance themselves from colonial encounters. Early Americans' incorporation and subordination of non-European medical philosophies authorized colonial medical knowledge as empirical and rational and facilitated conceptions of cultural differences between colonists, Native Americans, and Africans. My introduction examines medical encounters in the context of early modern medical philosophies and rhetorical practices. Chapter one examines how Thomas Hariot mixed Algonquian theories that disease originated in "invisible bullets" with Paracelsian medical philosophies, connecting seeing and knowing in his true report. Chapter two examines Pilgrim Edward Winslow's appropriation and subordination of shamans' medical practices to provide firsthand accounts of New World wonders in his providence tale. Chapter three examines the 1721 inoculation controversy in the context of Africans' testimony about inoculation, which minister Cotton Mather transcribed to connect words and things in his plain style, and which physician William Douglass satirized to reveal the gap between slaves' words and the true, dangerous nature of inoculation. Chapter four examines how James Grainger incorporated obeah, Africans' medico-religious practices, into his georgic poem to produce images of productive slaves and to construct new conceptions of obeah as witchcraft. Finally, the conclusion examines the ways in which colonists' disavowal of Native and African knowledge as magical continued to haunt U.S. Americans' literary practices, as seen in Arthur Mervyn's gothic tale of his encounter with a healthy black hearse driver during a yellow fever epidemic and Richard Allen and Absalom Jones' argument that blacks possessed superior knowledge of the epidemic.