The present study looks closely at the mosaic pavements of Delos and Pompeii, dated in the late 2nd and early 1st centuries B. C., in an attempt to account for the great differences in form, function, and technique observable in the genre. The earliest mosaics of Pompeii are of opus signinum, a cement embellished with designs picked out in white marble tesserae. Also common are pavements of irregularly cut stones and opus sectile. Contemporary pavements in Delos are polychrome, tessellated and concentrically arranged with decorative frames surrounding central, often figural, panels. Threshold mosaics at Delos are figural and have only a casual relation to the main pavement of the room. At Pompeii they are geometric and serve to distinguish functional areas of the house or room. At Delos finer materials are used for the central portion of the pavement; at Pompeii the material of the pavement is uniform over the entire surface. Finally, at Delos lead strips are used to outline some geometric motifs, a technique unknown at Pompeii. These differences are attributable to the respective origins of the Pompeian and Delian pavements. The signinum floors of Pompeii can be traced to 3rd century B. C. Punic establishments in North Africa and Sicily. The appearance and technique of the Delian floors-including the use of lead strips-go back to pebble mosaics like those found in Olynthus, dating from the late 5th and early 4th centuries B. C., and Pella, dated in the late 4th century B. C. The continued adherence of Eastern and Western mosaicists to their distinctive traditions is reflected in Pompeii and elsewhere in Italy in the tessellated pavements of the 1st and 2nd centuries A. C., which translated into black and white the designs characteristic of the early signinum pavements. The Eastern type of centralized, polychrome pavement can still be seen in the 1st century A. C. at Olympia, Corinth and Antioch, long after the East had submitted to Roman domination.