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This paper reviews genetic studies undertaken to generate an accurate phylogeny of killer whale (Orcinus orca) lineages. Three phylogenies, distinct in branching order and timing of divergences, are discussed. Of the three phylogenies, two are based on mitochondrial DNA and show more ancient divergence times for killer whale lineages. The third phylogeny, based on nuclear DNA, indicates that killer whales diversified more recently. The differing phylogenies have differing implications for biogeographic inference and for species assessments. The nuclear based phylogeny suggests that killer whale lineages diverged in sympatry while the mitochondrial based phylogenies as well as an empirical study indicate that the divergences more likely occurred in allopatry. The mitochondrial based phylogenies also support revision of killer whale taxonomy as there is indication that killer whales constitute multiple species and subspecies instead of a single species. The types of research that would be helpful in confirming hypotheses based on the phylogenies are discussed.