In the early 1880s, a finely carved Maya shell picture plaque was found at the Toltec capital of Tula, central Mexico, and was subsequently acquired by The Field Museum in Chicago. The shell was probably re-carved in the Terminal Classic period and depicts a seated lord with associated Maya hieroglyphs on the front and back. Here the iconography and glyphic text of this unique artifact are examined, the species and habitat of the shell are described, and its archaeological and social context are interpreted. The Tula plaque is then compared with Maya carved jade picture plaques of similar size and design that were widely distributed throughout Mesoamerica, but were later concentrated in the sacred cenote at Chichen Itza. It is concluded that during the Late Classic period, these plaques played an important role in establishing contact between Maya lords and their counterparts representing peripheral and non-Maya domains. The picture plaques may have been elite Maya gifts establishing royal alliances with non-local polities and may have become prestige objects used in caches and termination rituals.