Right whale dolphins are cetaceans belonging to the genus Lissodelphis. It contains the Northern Right Whale Dolphin (Lissodelphis borealis) and the Southern Right Whale Dolphin (Lissodelphis peronii). These cetaceans are predominantly black, white beneath, and one of the few without a dorsal fin or ridge. They are smaller members of the delphinid family, oceanic dolphins, and very slender. Despite scientists being long acquainted with the species (the Northern species was identified by Peale in 1848 and the Southern by Lacépède in 1804), little is known about them in terms of life history and behaviour.

Both species have slender bodies, small, pointed flippers and a small fluke. Conspicuously, neither species has a dorsal fin. The Northern Right Whale Dolphin is the only dolphin in the Pacific with this property. Similarly, the Southern is the only finless dolphin in the southern hemisphere. The two species can be readily distinguished (apart from the geographical separation in their ranges) by the extent of the whiteness on the body. Both have white bellies; however, the area of white coloration on the Southern species covers much more of the body - including the flanks, flippers, beak and forehead.

Right whales are three species of large baleen whales consisting of the genus Eubalaena in the family Balaenidae of order Cetacea. Their bodies are very dark gray or black and rotund.

A popular explanation for the name "right whales" is that they were the "right" ones to hunt, as they float when killed and often swim within sight of shore. They are quite docile, and do not tend to shy away from approaching boats. As such, they were hunted nearly to extinction during the active years of the whaling industry. This origin is apocryphal, however. In his history of American whaling, Eric Jay Dolin writes: "Despite this highly plausible rationale, nobody actually knows how the right whale got its name. The earliest references to the right whale offer no indication why it was called that, and some who have studied the issue point out that the word 'right' in this context might just as likely be intended "to connote 'true' or 'proper,' meaning typical of the group.""

Genetic evidence appears to have settled a long-standing question about whether to include the largest, the Arctic-dwelling bowhead whale, with the rest. Although all four are included in the taxonomic family Balaenidae, that whale is not included in the genus Eubalaena, and will therefore not be covered here.