McMurdo Sound is a small marginal basin located in the southwestern portion of the Ross Sea. The sound has been under the influence of either polar glacial or polar interglacial conditions since late Oligocene time. A detailed study of cores and high-resolution seismic data collected in McMurdo Sound was conducted to improve our understanding of the facies architecture resulting from sedimentation under polar interglacial conditions. Sedimentary sequences deposited within a marginal basin, under polar interglacial and temperate glacial regimes, can be distinguished by the presence of a diverse array of facies and an absence of thick and widespread clayey silt facies in the polar interglacial deposits. Thirteen facies have been observed in the cores recovered from polar interglacial deposits in McMurdo Sound. Facies relationships within the sound are so complex that statistical methods are required to determine the nature of the significant vertical and lateral associations. Sedimentation on the eastern side of the sound is characterized by deposition of sediment gravity flow deposits. Thickly bedded turbidites, cohesionless debris flows, and density-modified grain flows have been deposited on and at the base of the eastern slope of the sound, while thinly bedded, coarse-grained, and fine-grained distal turbidites occur in the central basin. Within the Erebus Basin, sedimentary deposits consist primarily of diatomaceous ooze and mud, and coarse-grained ice-rafted debris. The facies of the basin also show an intertonguing relationship with the sediments of the eastern and western slopes of the sound. Sedimentation on the western slope of McMurdo Sound is dominated by deposition of: (1) ice-rafted eolian debris from the south; (2) primary eolian deposition; (3) turbidites with sources on the western shelf and slope; and (4) a minor amount of ice-rafted eolian debris from the west. Deposition of ice-rafted debris from the west and coarse ice-rafted debris from the McMurdo Ice Shelf comprise the primary modes of sedimentation on the upper portion of the western slope and the western shelf. Although deposition of debris from the McMurdo Ice Shelf is associated primarily with the western shelf, it can also be found in any of the other environments mentioned above. The upper portions of cores from northern McMurdo Sound contain the east-to-west lithofacies variation described above, but the lower portions of these cores contains a quartzose facies that represents sedimentation in front of the grounding line of an outlet glacier.