Atopic dermatitis (AD) is a chronic inflammatory skin disease affecting over 10% of human (sic) children, and it is the most common cause of occupational disability in adults. Atopic dermatitis also is seen commonly in companion animals, especially in dogs, in which its prevalence has been estimated to be about 10% of the canine population. Numerous similarities exist between canine AD and its human counterpart, suggesting the possibility that canine AD could be used as a model for the human disease. Dogs have been used in the past as model for human allergic diseases. The most popular model has been the Basenji–Greyhound, which develops a recurrent, nonseasonal, pruritic dermatitis and asthma. Skin lesions include lichenified plaques and inflammatory papules and nodules. These dogs also display airway hyper-reactivity, with changes in pulmonary mechanics similar to those of symptomatic, human asthma, and they exhibit a variety of immunologic abnormalities analogous to the human disease. Cats also have been reported to develop AD, but our understanding of the condition in this species currently is limited. Certain similarities appear to exist between feline and human AD; however, the feline condition has some peculiar clinical features, and for this reason it will be described separately. Finally, AD recently has been described in laboratory animals, notably the NC/ Nga mouse, which is thought by some authors to be a promising animal model for AD. The purpose of this article is to review the latest information available on AD in companion animals and in mice and describe how these spontaneously arising diseases might serve as models to improve our understanding of human AD.