Matthias Grunwald's world-famous Isenheim Altarpiece ranks among the most powerful expressionistic works of the Northern Renaissance. Characterized by great emotional force, exquisite handling of color and brilliantly interwoven subtleties of Christian iconography, the multi-paneled altarpiece has remained the object of intense scholarly interest and the main attraction of the Musee d'Unterlinden in Colmar, France. Ruth Mellinkoff offers an original analysis of the altarpiece, uncovering the late medieval popular beliefs that underlie its unusual visual content. She places its rich imagery within a tradition of Christian art, and stunningly, discovers Lucifer among the angels observing the Nativity.