Mosaic is a medium of art that may embody the most meaningful iconography in a culture's most important settings. In mosaics, small tiles or fragments of pottery (known as tesserae, diminutive tessellae) or of colored glass or clear glass backed with metal foils, are used to create a pattern or picture.

When Christian basilicas began to be purpose-built in the late 4th century, wall and ceiling mosaics were adapted to Christian uses. The greatest development of Christian mosaics unfolded in the Byzantine empire including its outpost the Exarchate of Ravenna and its territories in Sicily, and in its late rival Venice, where mosaic encrusts the exterior and interior of St Mark's.

The craft has continued through the ages, kept alive in the Eastern Orthodox tradition especially, and extending to Russia, where Moscow claimed to succeed Constantinople as the "Third Rome." Many modern examples of mosaic exist and contemporary artists are restoring known techniques to produce the best craftsmanship of mosaic iconography.