The legal and moral imperatives for incorporating indigenous knowledge into natural resource management are now widely recognized. Many consider the integration of indigenous knowledge to be an essential component of successful solutions for conserving resources valued by indigenous peoples, including marine mammals. The effective integration of indigenous knowledge requires an understanding of what it is. Indigenous elders from five very different parts of the world briefly explain their knowledge of local marine mammals including: ika-moana (large whales) of Aotearoa, New Zealand; dhangal (dugongs) of Torres Strait between northern Australia and Papua New Guinea; river dolphins and manatees of Amazonia; beluga whales, Atlantic walrus, bearded seals and harp seals of the Nunavik region of north Quebec in the Canadian Arctic; and sea otters, spotted or larga seals, northern fur seals and Steller sea lions of the Commander Islands, Russia. These accounts illustrate the complexity and temporal dynamism of indigenous knowledge. To help identify the themes in these accounts, we used an extension of Houde's typology (in Ecol Soc 12(2):34, 2007) of indigenous knowledge, which we envisaged as a hexagon with worldview at the core and cosmology, factual observations, management systems, past and present uses, ethics and values, and culture and identity on its faces. We hope that this chapter will help marine mammal scientists who work in research partnerships with indigenous peoples, to build trust, respect, and mutual understanding of each other's knowledge systems. This understanding should help marine mammal scientists to work successfully across the "cultural interface to achieve true progress in marine mammal conservation and coexistence."