Although many studies treat the causes and consequences of dispersal in mammalian populations, less attention has been given to the individuals that do not leave their birthplaces. Yet natal philopatry, which we define as continued residence on the natal home range past the age of independence from the parents, occurs in virtually all gregarious mammals. We here document its widespread occurrence among solitary species as well. By studying the distribution of natal philopatry across various ecological and life-history regimes we attempt to identify its ultimate causes. The variables that emerge as possibly important include adult turnover rates, habitat saturation, spatial patchiness of resources, advantages of familiarity with the natal home range, and reliance on extensive home range "improvements" such as burrow systems of food caches. The most interesting consequence of natal philopatry is the continued spatial association of kin into adulthood, a prerequisite for many phenomena common to gregarious s...