A rescue group or rescue organization is dedicated to pet adoption. These groups take unwanted, abandoned, abused, or stray pets and attempt to find suitable new homes for them. Many rescue groups are created by and run by volunteers, who take the animals into their homes and care for them—including training, playing, handling medical issues, and solving behavior problems—until a suitable permanent home can be found.

Rescue groups exist for most types of pet—for example, rabbit rescue or bird rescue, but are most common for dogs and cats. For animals with many breed types, many rescue groups specialize in specific breeds or groups of breeds. For example, for dogs, there might be local Labrador Retriever rescue groups, hunting dog rescue groups, large-dog rescue groups, as well as general dog rescue groups.

Animal shelters often work closely with rescue groups, because shelters who have difficulty placing otherwise healthy and pet-worth animals would usually rather have the animal placed in a home than euthanized; while the shelters might run out of room, rescue groups can often find more volunteers with space in their homes for temporary placement.

In the UK, both shelter and rescue organisations are described using the blanket term rescue, whether they have their own premises, buy in accommodation from commercial kennels, or operate a network of foster homes, where volunteers keep the animals in their homes until adoption.

Kennels that have a council contract to take in stray dogs are usually referred to as dog pounds. Some dog pounds also carry out rescue and rehoming work and are effectively rescue groups that operate a pound service. Some rescue groups work with pounds to move dogs to rescues. By law, a dog handed in as a stray to a UK pound must be held for 7 days before it can be rehomed or euthanized.

In the USA, there are three classifications for pet rescue:

* A municipal shelter is a facility that houses stray and abandoned animals, as well as animals that people can no longer care for, on behalf of local governments

* A no-kill shelter, which is usually a privately-operated organization with a physical location, such as a storefront or free-standing building. Their policies include the specification that no healthy, pet-worthy animal be euthanized

* Not-for-profit rescue organizations that typically operate through a network of volunteer foster homes. These rescue organizations are also committed to a no-kill policy as specified above.