This thesis examines the Lady of the Lake as an active chivalric player in the thirteenth century Lancelot-Grail Cycle (also known as the Prose Lancelot) and in Thomas Malory's fifteenth-century Le Morte Darthur. To study the many codes of chivalry, particularly in regard to women, I use two popular chivalric handbooks from the Middle Ages: Ramon Lull's Book of Knighthood and Chivalry, Geoffroi de Charny'sKnight's Own Book of Chivalry. Traditionally, the roles of women in medieval chivalry are passive, and female characters are depicted as objects to win or to inspire knights to greatness. The Lady of the Lake, I argue, uses her supernatural origins and nature to break with female chivalric conventions and become an instructress of chivalry to King Arthur's knights. As a purely human character, her power would be limited. As a guardian fairy and/or enchantress, the Lady is allowed to exercise more autonomy