A diptych is a painting in two parts, usually joined together by hinges so that it can be closed like a book. Most usually these were small religious paintings or altarpieces used for private devotion. Triptychs are in three settings, with the outer sections foldable to cover the cetral panel, while more complex, multi-panelled altarpieces are known as polyptychs. Many panel paintings took the diptych form from the Middle Ages onwards – the Wilton Diptych is a rare survival from this period – and it was a common format in early Netherlandish painting.