American animal shelters house between six and eight million dogs and cats each year. The question of what to do with millions of healthy but unwanted animals has animated sheltering from the start. Responses reveal how the presence of animals in society shapes institutions, laws, and policies. Pounds emerged to resolve the problems posed by stray animals. Concern for animal welfare created the need and justification for shelters, as humane alternatives to the pounds. Trends in pet-keeping and veterinary medicine shaped twentieth-century sheltering practices, as shelter populations evolved from strays to unwanted pets. Recently, criticism of high euthanasia rates engendered no-kill shelters. The social and cultural significance of animal sheltering lies in the light it sheds on the changing value of companion animals.