A pet harness is a device consisting of straps of straps that run almost all the way around the animal's torso and which are held together using side release buckles.

These harnesses usually have a strap on the chest in front of the forelimbs, a strap on the torso behind the forelimbs and a strap in the middle connecting the two. There is a D-ring to fit (pet tags and) belt clips, and they are most commonly used to restrain animals, but dogs also wear them specifically to assist disabled people or to haul people and objects. This article also describes lifting harnesses for dogs with disabilities.

Some come in different sizes, although many are adjustable and come with a triple slider to loosen or shorten the length of the straps. Straps may come in a variety of different colours and some have a reflective coating.

The most common use of a pet harness is for the physical restraint of an animal. When used in this way, the harness is worn with the leash; one end of the leash has a metal clip that attaches to a loop on the harness, while the other end is usually a loop held by a person.

While the collar only goes around the neck, the harness has loops that go around the chest. This design allows for the distribution of forces, thus reducing the pressure exerted on the animal's windpipe, and therefore the risk of strangulation is significantly reduced. The harness is much less likely to allow the animal to slip out than if the collar were worn. As a result, collars have largely been replaced by harnesses.

Pet clothing often has a properly placed buttonhole for the D-ring of a harness worn underneath the clothing. Some harnesses, such as those worn by police dogs, may have a handle so that they can be restrained (or lifted) more securely by hand. Such harnesses (or vests) may be marked and have ballistic padding.