The distribution of the harbour porpoise Phocoena phocoena (L.). is re-examined using a compilation of all available recent information. Three isolated major populations of this species exist: in the North Pacific, North Atlantic and in the Black Sea-Sea of Azov, distinguishable by differences in morphology and meristic characters. Incorporating the scheme originally proposed by D. B. Yurick in 1977, a provisional series of what appear to be relatively distinct subpopulations within the North Pacific and North Atlantic are delineated. The Black Sea-Sea of Azov population is considered to represent a single population. The proposed North Pacific subpopulations are those of the eastern Bering Sea, south Sea of Okhotsk and coastal waters of northern Japan, and the western seaboard of North America from the Gulf of Alaska to south California. The proposed subpopulations in the North Atlantic region include those of eastern Newfoundland and western Davis Strait, West Greenland, the Gulf and Estuary of the St. Lawrence, southern Nova Scotia to North Carolina, southeast Greenland, Iceland and the Faeroes, Ireland and west Britain, Biscay and the English Channel, the North Sea, the Baltic Sea, the Norwegian coast, Barents Sea-White Sea, the Iberian Atlantic coast, and the West African coast. Factors which appear to segregate these subpopulations include geographical intrusions of land masses or deep ocean basins, migratory patterns, ice fields, and availability of coastal habitat suitable for the species. All proposed subpopulations must be considered provisional, and some degree of interchange is probable: on the other hand there is significant evidence from some areas for year-round residency and localization. All information on direct and indirect recent catches has been assembled, tabulated and discussed. The Baltic Sea and Black Sea-Sea of Azov populations would appear to be in critical condition, and that of the Mediterranean, probably never very large, appears to be virtually extinct. Heavy catches, relative to probable population size, are made from the West Greenland, eastern Newfoundland, North Sea and southern Nova Scotia to North Carolina populations: most mortality is from net fisheries. The only large direct take occurs in coastal waters of West Greenland, now that the Turkish hunt has ceased.