A drift whale is a cetacean mammal that has died at sea and floated into shore. This is in contrast to a beached or stranded whale, which reaches land alive and may die there or regain safety in the ocean. Most cetaceans that die, from natural causes or predators, do not wind up on land; most die far offshore and sink deep to become novel ecological zones known as whale falls. Some species that wash ashore are scientifically dolphins, i.e. members of the family Delphinidae, but for ease of use, this article treats them all as "drift whales". For example, one species notorious for mass strandings is the pilot whale, also known as "blackfish", which is taxonomically a dolphin.

In historical sources, it is not always clear whether a given cetacean washed up alive or dead, but the term "drift whale" focuses on the benefits of its carcass – meat, blubber, fat, and other products – to the people who claimed it. Nowadays, when a dead whale washes up on a beach, often the authorities are required to dispose of it as a potential hazard to human health, so the resource implications go the other way: a drift whale is no longer a benefit to a community, but an expensive disadvantage.

Many cetacean species have been documented as drift whales, but some are more common than others. In New England, for example, the carcasses of fin, humpback, sperm, right, and pilot whales, as well as dolphins, are most likely to drift ashore. Some species have a naturally high buoyancy, and float when they are dead, aided by the gases of putrefaction.

Whales that live in the pelagic ocean, far from the continental shelf, are less likely to wash up ashore than coastal species. Once these deep-sea animals do find themselves in shallower waters, however, they may run into difficulties, as the gradual shelving of the shoreline is thought to play a role in confusing their sense of echolocation. Sperm whale strandings are known to have occurred in the North Sea for centuries, and the incidents may be increasing with louder ship noise.

Aside from the whaling industry, most cetaceans have no predators other than the orca (killer whale) and certain large sharks (such as the dusky), which in both cases tend to attack in groups and focus on one young whale. Some drift whale carcasses show injuries consistent with attacks from these species, or, in modern times, with ship strikes (e.g., trauma from a propeller). Another obvious and visible cause of traumatic death is cetacean bycatch, i.e., entanglement with fishing gear, which kills tens of thousands each year, according to the International Whaling Commission.

Other carcasses show no visible injury, and theories about why the animals died include the possibilities discussed for live strandings (especially active sonar) as well as illness and malnutrition. Sometimes a necroscopy is performed, which can reveal the cause of death, such as ingestion of plastic pollution and other Marine debris.

Certain beaches are well known as likely spots for whales, and other gifts from the sea, to wash up: drift seeds, driftwood, and latterly sea glass and even messages in bottles. Modern recreational beachcombers use knowledge of how storms, geography, ocean currents, and seasonal events determine the arrival and exposure of rare finds; the same applies to those looking out for drift whales.

Eponymous coastal features include Drift Whale Bay within Brooks Peninsula Provincial Park on the Pacific Coast of Vancouver Island. Saint-Clément-des-Baleines on the Atlantic coast of France is named after its stranding beach.