This chapter presents mousepox as a model for research in several fields, notably the pathogenesis of generalized infections, experimental epidemiology, and the cellular immune response. It also discusses the natural history of mousepox in laboratory colonies of mice and the measures that can be used for its control. It further explores, in a less detailed manner, some of the results that have emerged from the use of the disease as a model infection by Australian virologists and immunologists. Among the 16 named families of viruses that infect vertebrate animals, viral species that occur as natural infections of mice are found in all except five, and mice can be artificially infected with viruses from each of these families as well. Two distinct species of poxvirus produce natural infections of rodents: infectious ectromelia, or mousepox virus, and the Turkmenia rodent poxvirus, which is a close relative of cowpox virus. Both of these are orthopoxviruses and show strong serological cross-reactivity with other members of the genus Orthopoxvirus. Early workers described two forms of the disease: (1) a rapidly fatal form in which apparently healthy mice died within a few hours of the first signs of illness and showed extensive necrosis of the liver and spleen at autopsy and (2) a chronic form characterized by ulcerating lesions of the feet, tail, and snout.