AbstractDominance hierarchies have been well studied in myriad terrestrial animals, but surprisingly little is known about hierarchies in marine invertebrates; examples are limited to a few species of decapod crustaceans and cephalopods. Is the marine environment less conducive to the establishment of dominance hierarchy structures, or does this just underline the lack of detailed behavioral information about most marine invertebrates? In this review, we highlight the published information about marine invertebrate dominance hierarchies, which involve ranks established through fights or displays. We focus on the method of hierarchy formation, examine the ecological implications of this population structure, and compare the habitat and behavioral characteristics of species that exhibit this behavior. Because dominance hierarchies can influence habitat use, population distributions, energetics, mating, resource exploitation, and population genetic structure, it is crucial to understand how this trait evolves and which species are likely to exhibit it. A better understanding of marine invertebrate hierarchies could change the way we think about population dynamics of some species and could have important implications for fisheries, conservation, or even modeling of social and economic inequality.