An animal sanctuary is a facility where animals are brought to live and to be protected for the rest of their lives. There are five types of animal sanctuaries determined by the species of the residents: companion animal sanctuaries, wildlife sanctuaries, exotic animal sanctuaries, farmed animal sanctuaries, and cetacean sanctuaries.

Unlike zoos, sanctuaries do not breed animals, exhibit animals for human entertainment, offer visitors the chance to touch animals, or use animals commercially. Unlike animal shelters, sanctuaries typically do not seek to find new human homes for animals; they provide a safe haven for each animal until their natural death. In some cases, an establishment may have characteristics of both a sanctuary and a shelter, however, assisting in rehoming when needed. Animals are not bought, sold, or traded, nor are they used for testing or experimentation. Additionally, no parts of nor secretions from the animals, such as eggs, wool, or milk, are commodified. The resident animals are given the opportunity to behave as naturally as possible in a protective environment.

What distinguishes a sanctuary from other institutions is the philosophy that the residents come first. In a sanctuary, every action is scrutinized for any trace of human benefit at the expense of non-human residents. Sanctuaries act on behalf of the animals, and the caregivers work under the notion that all animals in the sanctuary, human and non-human, are of equal importance.

A legitimate sanctuary avoids activities that place animals in an unduly stressful situations. Thus, they do not sell daily access to the animals, in the manner of zoos. Most sanctuaries are also not government-funded and are usually nonprofit. Public help is accepted by sanctuaries in the form of volunteering, monetary contributions, donations of food and materials, spreading the word, and in some cases, adoption.

One of the most important missions of sanctuaries, beyond caring for the animals, is educating the public. The ultimate goal of many sanctuaries is to change the way that humans think of, and treat, non-human animals.

On the basis of the types of animals being cared for, sanctuaries are of five types:

A wildlife sanctuary provides food, protection, and veterinary care for wild animals that have been rescued from zoos, circuses, and other abusive situations. Some wildlife sanctuaries provide care for multiple species, while others focus on a single species. Sanctuaries that care for more than one species may allow interspecies interaction, but keep predators segregated from prey.

Farmed animal sanctuaries (FAS) provide care, shelter and advocacy of farmed animal species such as chickens, cows, goats, fish, horses, pig, turkeys, and sheep. The farm sanctuary layout tends to resemble traditional farms however functions differently. FAS as a movement began with Gene Baur, the co-founder of Farm Sanctuary, the first official farm sanctuary that opened in 1986. The daily tasks of a FAS involve the primary guardians, volunteers and at time visitors. Each day is structured by routines such as feeding, care and health procedures, as well as cleaning and maintenance. Points of conflict for sanctuaries include human intervention in matters of sterilizing animals and species segregation. Moreover, effective altruists have critiqued the efficiency of FAS's ability to reduce animal suffering as demonstrated in the "arithmetic of compassion", a utilitarian measure of advocacy that applies mathematical formulas to reduce the most suffering in light of individual lives. Jon Bockman of Animal Charity Evaluators, states, "expending too many resources on direct rescue results in less money directed toward education and a lower overall impact in helping animals, and all advocates should give consideration to this concern when deciding how best to help animals". FAS has, in some ways, evolved to more actions such as re-homing to increase sanctuary capacity and rescuing farmed animals in criminal or domestic cases.