Abstract: The miniatures in the Hours of Mary of Burgundy have been chronically understudied despite its acclaim. The present study aims to construct a comprehensive explanation of the spiritual use, theological implications, and devotional context of the illusionistic miniatures in The Hours of Mary of Burgundy by first examining the theological context of the manuscript’s creation before completing a deep iconographic, situational, and psychological analysis of the miniatures. Firstly, the present study argues that the devotio moderna was deeply connected to the mystic tradition, and that the beliefs and practices of mysticism and the devotio moderna inform the creation of the Hours of Mary of Burgundy. Secondarily, the present study argues that the miniatures in the hours are effective tools of devotion to the owner through their illusionistic naturalism, reflexive structure, transitive quality, and reliance on user interaction. Ultimately, therefore, the miniatures each have components that act as mirrors and windows to the physical, emotional, spiritual, and psychological state of the original owner, Mary of Burgundy herself. Lastly, the present study argues that books of hours as objects function as mirrors and windows as well.