This dissertation offers the first full-length study of the Haarlem painter Jan Jansz Mostaert (ca. 1494–1552/53). Although Karel van Mander, the “Vasari of the north,” included a biography of Mostaert in his famous 1604 Schilder-boeck (Book of Painters), Mostaert’s oeuvre became dissociated from his name over the ensuing centuries and was only reattributed to him in the late 1800s and early 1900s. Since then, research on Mostaert has been piecemeal, with the most attention paid to identifying the event portrayed in his Landscape with an Episode from the Conquest of America in Amsterdam. Although the Conquest of America may be his most unique painting, one finds throughout Mostaert’s body of work a painter creatively grappling with the challenges of a turbulent age, including a changing understanding of religious images, the shifting status of the artist, the burgeoning market for art, and a globalizing Europe. Through close examination of the paintings—several of which had been addressed only in passing in existing scholarship—and, where available, technical and archival data, this dissertation offers an assessment of Mostaert’s distinctive working methods and how his Late Gothic style changed over his long career, with a focus on his iconographic originality.