Dermatophytosis is an infection of keratinized tissue (skin, hair, and claws) by one of the three genera of fungi collectively called dermatophytes—Epidermophyton, Microsporum, and Trichophyton. (Also see Fungal Infections.) These pathogenic fungi are found worldwide, and all domestic animals are susceptible. In developed countries, the greatest economic and human health consequences come from dermatophytosis of domestic cats and cattle. A few dermatophyte species are soil inhabitants (geophilic), eg, M gypseum and T terrestre, and cause disease in animals that are exposed while digging or rooting. Other species are host-adapted to people (anthropophilic), eg, M audouinii and T rubrum, and infect other animals rarely. The most important animal pathogens worldwide are M canis, M gypseum, T mentagrophytes, T equinum, T verrucosum, and M nanum. These species are zoonotic, especially M canis infections of domestic cats and T verrucosum of cattle and lambs. The zoophilic species are transmitted primarily by contact with infected individuals and contaminated fomites such as furniture, grooming tools, or tack. Exposure to a dermatophyte does not always result in infection. The likelihood of infection depends on several factors, including the fungal species, host age, immunocompetence, condition of exposed skin surfaces, host grooming behavior, and nutritional status. Infection elicits specific immunity, both humoral and cellular, that confers incomplete and short-lived resistance to subsequent infection or disease. New information concerning dermatophytic virulence factors, notably secreted proteases involved in the invasion of keratin, aspects of host immune response against dermatophytes, and new molecular tools available for studying dermatophytes should hasten development of safe and effective vaccines against dermatophytosis in species without vaccination options.