Some species are marine, e.g., the Atlantic sturgeon Acipenser oxyrhyncus; some ascend rivers to spawn; and some (the largest of inland fish) are found in landlocked waters. The largest species is the Russian sturgeon, or beluga (A. huso), of the Caspian and Black seas; it reaches a length of 13 ft (396 cm) and a weight of up to a ton (900 kg). The Pacific sturgeon (A. transmontanus) may weigh over half a ton (450 kg) and attain a length of 12 ft (366 cm). The green sturgeon is a smaller Pacific variety, and the common sturgeon is found in coastal waters and rivers of Europe and E North America. Other American species are the rock, or lake, sturgeon (A. fulvescens) of the Great Lakes and the Mississippi valley and the shovel-nosed sturgeon, or hackleback (Scaphirhynchus platorynchus; 3 ft/91 cm), also of the Mississippi valley.

Smoked sturgeon is considered a delicacy in many areas, and sturgeon eggs are the source of the better grades of caviar, sometimes in combination with eggs of the paddlefish, a close relative. Russia, Iran, and other countries surrounding the Caspian Sea have undertaken conservation measures, including aquaculture and setting catch quotas, to save the threatened Russian sturgeon from extinction, but declines in Eurasian species of sturgeon have led to several suspensions of the international trade in wild caviar from the region since 2001. Sturgeon are also raised on fish farms in a number nations outside the Caspian basin.

Sturgeons are classified in the phylum Chordata, subphylum Vertebrata, class Osteichthyes, order Acipenseriformes, family Acipenseridae.