True's beaked whale (Mesoplodon mirus) is one of 21 species of beaked whales (Hyperoodontidae or Ziphiidae), medium-sized whales with distinctive, long narrow beaks and dorsal fins which are set far toward the posterior. This species is a marine mammal within the order of cetaceans.

True's beaked whale is a toothed whale and can be recognised as such by the single blowhole as well as the presence of teeth (rather than baleen). Because of the highly disjunctive distribution patches of True's beaked whale, it is possible that the northern and southern hemisphere temperate ocean populations are actually distinct species or subspecies. Threats to the species include bycatch and underwater noise pollution.