Population structure can reveal the diversity, gene flow, and dispersal of a species. This information can be used to make management decisions and reveal fundamental aspects of an organism's biology. Distinct intrinsic (e.g., biological characteristics) and extrinsic (e.g., geographical and historical events, environment, human pressures) factors can influence population structure, with significant differences among species. However, detection of population structure in migratory lamprey species can be difficult to detect due to their lack of natal homing; this is particularly the case for anadromous lampreys, with their potential for wide dispersal at sea during their parasitic feeding stage. We review phenotypic and genetic markers, as well as the methods that have been used to assess population structure in lampreys, and discuss the relative strengths and limitations of each. Structure has been detected in several anadromous species using some of these methods, even without homing in these species, but we briefly contrast the weak population structure observed in anadromous species with the stronger structure observed in freshwater-resident lamprey species (particularly non-migratory brook lampreys). We relate lamprey population structure to species-specific ecological traits, such as juvenile dispersal tendencies, and provide case studies of six species. Delineation of appropriate management units in migratory lamprey species is important for conservation and management. (C) 2021 The Authors. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research.