Orcinus species = O. orca binomial = Orcinus orca binomial_authority = Linnaeus (Carolus Linnaeus), 1758 synonyms = Orca gladiator range_map = Killer Whale Range Map.svg range_map_alt = A world map shows killer whales are found throughout every ocean, except parts of the Arctic. They are also absent from the Black and Baltic Seas. range_map_caption = Orcinus orca range (in blue)

The killer whale (Orcinus orca), commonly referred to as the orca—and, less commonly, blackfish—is the largest species of the oceanic dolphin family. They are found in all oceans, from the frigid Arctic and Antarctic (Antarctica) regions to tropical seas. Killer whales have a diverse diet, although individual populations often specialize in particular types of prey. Some feed exclusively on fish, while others hunt marine mammals such as sea lions, seals (Earless seal), walruses and even large whales. Killer whales are regarded as apex predators, lacking natural predators.

Killer whales are highly social (social animal); some populations are composed of matrilineal family groups which are the most stable of any animal species. Their sophisticated hunting techniques and vocal behaviors, which are often specific to a particular group and passed across generations, have been described as manifestations of culture.

The IUCN currently assesses the orcas conservation status as data deficient because of the likelihood that one or more killer whale types are separate species. Some local populations are considered threatened (threatened species) or endangered (endangered species) due to prey depletion, habitat loss, pollution (by PCBs (Polychlorinated biphenyl)), capture for marine mammal parks, and conflicts with fisheries (fishing). In late 2005, the killer whales known as the "southern resident killer whales" were placed on the U.S. Endangered Species list.

Wild killer whales are not considered a threat to humans, harvnbCarwardine2001p=19 although there have been cases of captives killing or injuring their handlers at marine theme parks (marine mammal park). Killer whales feature strongly in the mythologies of indigenous cultures. In Western cultures, it has had a reputation for being a fearsome predator.