The Animal Welfare Institute (AWI) was founded in 1951 by Christine Stevens as a non-profit, charitable organization with the intention of working to reduce the amount of pain and fear that humans inflict on animals. The immediate focus of the AWI in the 1950s and 1960s was the cruelty to which animals were subjected in research laboratories and other experimental environments. Since that time, the AWI has expanded its focus to also monitor animals in the wild (land and ocean, giving special attention to those species which are endangered), on farms, and in various other captive environments, such as zoos, circuses, and domestic situations.

To promote these aims, the Society for Animal Protective Legislation (SAPL) was subsequently founded by Stevens in 1955. When SAPL was founded, only two federal laws to protect animals existed; with its founding, SAPL became the first non-profit organization in the United States dedicated to the passage and promotion of local, federal, and international legislation concerning animal welfare. Begining in 1958, SAPL has aided in the ratification of fifteen federal laws and nine strengthening amendments, while also working to combat opposing legislation.

SAPL existed as a separate, sister organization of the AWI until 2003 (although both were run by Stevens); tax law changes in that year allowed SAPL to become a division of the AWI. To promote animal welfare, SAPL researches animal-specific issues and then prepares information for members of Congress and their staff.

Christine Stevens acted as president of AWI from the time of founding until her death in 2002. Today the AWI is run by a group of directors, officers, and other committees of scientific personnel. The AWI is headquartered in Washington, D.C.