A taxonomic and life history study of the inconnu was carried out on populations from the Kobuk, Chatanika, and upper Yukon Rivers, and Selawik, Alaska. Data on 24 morphological measurements and 11 meristic counts show little difference among: 1) males and females; 2) young and older inconnu; and 3) fish from the upper Yukon River, Chatanika River, Selawik, and Kobuk River in Alaska and the Ob River, USSR. Based on close agreement of these counts and measurements, the inconnu in Alaska is designated as Stenodus leufifhthys nelma (Pallas). For arctic fish, the inconnu exhibits a rapid growth rate. Growth rates for males and females are similar, but females live longer than males. Alaskan inconnu become sexually mature quite late in life (for Selawik males, 9 years; females, 10 years). Spawning behavior is described. Spawning occurred in the Kobuk River above Kobuk the last days of September at water temperatures betwen 1/4 and 4.6 C. Older inconnu are mainly piscivorous while the younger fish feed on invertebrates and fish. The least cisco, Coregonus sardinella, was the main food item of the Selawik inconnu. The estimated catch in Northwest Alaska in 1965 was between 34,200 and 37,000 fish, 85% of which were taken for subsistence.