“This remarkable, lucid book takes on a big and complex subject, still somewhat invisible to scholarship. It fully reconsiders a major late medieval art form: the triptych format of hinged altarpieces. The triptych—along with its components, oil paint technique and refined oak carving—rose to Golden Age prominence in fifteenth-century Flemish art. Offering an impressive survey of this great artistic achievement, Opening Doors truly lives up to its name and contributes fresh new interpretations. Scholars and their students will use this book as a standard work for many years to come.”—Larry Silver, University of Pennsylvania