Essays in Context: Unfolding the Netherlandish Diptych serves as an excellent companion to the exhibition catalogue for Prayers and Portraits: Unfolding the Netherlandish Diptych, also edited by John Oliver Hand and Ron Spronk, along with Catherine Metzger (Washington, DC: National Gallery of Art; and New Haven: Yale University Press, 2006). The product of two roundtable discussions, its thirteen fine scholarly essays present a rich array of related topics. In the first essay, Victor Schmidt addresses the development of diptychs prior to 1400. He begins by showing that the term “diptychum” or “diptycha” originally referred to a set of joined tablets or writing on a paper folded in two. Throughout the Middle Ages, diptychs were made with a variety of materials, including ivory, wood, and metal. Diptychs, frequently hinged, combined two panels of equal size. This format provided the advantage of protecting internal imagery, while promoting iconographical comparisons between panels. Although diptychs are often associated with private devotion, Schmidt rightfully points to some of the dangers in underestimating their role in public worship. Lorne Campbell offers a general discussion of diptychs with donor portraits. Although often paired with sacred figures, portraits could also serve secular purposes. For instance, Isabel of Castile...