Two seasonal volumetric temperature/salinity diagrams have been prepared for the waters of the Middle Atlantic Bight from Nantucket Shoals to Cape Hatteras, to a depth of 200 m and extending as much as 130 km beyond the edge of the continental shelf. Total volume included is 23,145.6 km3, of which about half is slope water, more saline than 35‰. Most of it is in a distinctive subsurface maximum region near 13°C, which is named the upper slope water thermostad. The less saline shelf water has two modes divided by a minimum near 33.6‰. The fresher mode, associated with shallow depths, is identified as coastal water; that from 33.6–35‰ is called shelf edge water, and much of it is found seaward of the shelf break. There is very little seasonal change in the total volume of shelf water but its geographical distribution varies, showing the effects of spring runoff and suggesting a summer influx of slope water in the northern portion of the bight. Comparison with a similar census for the Gulf of Maine and shelf waters to the east shows some overlap but little evidence of substantial exchange.