The diptych format—comprising two panels hinged together so they can be opened and closed like a book—was prevalent in Netherlandish art and depicted subjects ranging from secular portraiture to religious personages and stories. This book, the first ever devoted to the topic, examines approximately 40 pairs of Netherlandish paintings from the 15th and 16th centuries. Featuring works by Jan van Eyck, Hugo van der Goes, Hans Memling, and Rogier van der Weyden, among others, the book also covers a wide range of themes, including painting techniques, workshop practice, and the Netherlandish art market of the time. With discussions on each painting, this catalog reunites a number of diptychs that had long been separated. Texts incorporate new information based on extensive examinations and a vast archive of original technical images, many of which are reproduced.