We investigated the social interactions and spatial organization of the Japanese badger (Meles anakuma) using radiotelemetry. Fifty-two individuals (29 males and 23 females) were trapped and marked (tattooed) between 1990 and 1997 from a population with a density of 4 individuals/km². Twenty-one of these individuals were subsequently radiotracked. The average home-range size of males expanded from an average of X̄ = 33.0 ha ± 18.1 SD in the nonmating season to 62.6 ± 48.2 ha in the mating season, and was significantly larger than the home-range size of females (15.2 ± 6.3 ha in the mating season; with a lack of data on individual female home-range–size change between seasons). We posit that this range expansion by males occurred to encompass the key resource of estrous females during the breeding season; thus, males exhibited a flexible home-range strategy. Females with cubs had home ranges exclusive of other adult females, configured around areas rich in food resources, indicative of intrasex territoriality. This obstinate strategy, under the constant territory size hypothesis, likely serves to ensure a reliable supply of food resources (as determined by resource dispersion) for cub rearing. Eleven of 36 cubs born during the study remained in their natal range until the next spring and we observed 1 of 5 instances of matriarchal territory inheritance. Microsatellite DNA analysis indicated that the basic social unit was composed of the mother and cub(s), with less-related males providing gene flow. This mother–cub unit, with the retention of nonbreeding juveniles or young adults, or both, along with the loose affiliation of breeding males, informs understanding of the development of group-living, subject to ecological circumstances, in the genus Meles and broadens understanding of the evolution of carnivore sociality.