Dolphins and porpoises both belong to the Suborder Odontoceti. Members of this order possess teeth, a single blowhole, and often exhibit sexual dimorphism. Odontocetes also possess bilaterally asymmetrical skulls that often support a well developed melon, or bulbous forehead. Most odontocetes are more social than other groups of cetaceans and use echolocation for navigation.

These similarities often lead to a misconception about the two odontocetes. Although the terms "dolphin" and "porpoise" are often used interchangeably, they describe two different groups of cetaceans. Dolphins belong to the Family Delphinidae, while porpoises belong to the Family Phocoenidae. Many external characteristics exists that are useful in distinguishing between these two families. For example, the extended beak present in most delphinids is absent in most phocoenids . Similarly, most phocoenids lack a melon, while the bulbous forehead is often observed in delphinids.

In addition, the dorsal fin of delphinids is often hooked or curved, while the dorsal fin in most phocoenids is triangular in shape. Some members of both families lack dorsal fins altogether. Also, merely the first two cervical are fused in delphinids, while the first six cervical are fused in phocoenids. This increased number of fused cervical limits the range of mobility in the porpoise neck.Equally, the teeth of dolphins and porpoises are distinct from one another. Delphinids possess homodont conical teeth in both jaws, while phocoenids posses spatulate, or spade-shaped, teeth in both jaws.

In contrast, members of the Family Phocoenidae are rarely observed in groups of more than one or two individuals. Likewise, delphinids can often be seen performing acrobatics, such as breaching, or leaping out of the water and returning with a splash, while such acts are rarely ever observed by phocoenids. Similarly, many members of Family Delphinidae can be observed bow-riding, or riding on the pressure wave of a large ship or whale, on passing vessels. Unlike delphinids, members of the Family Phocoenidae are rarely seen bow-riding. In fact, many species within this family appear to be frightened of ships and large cetaceans.