A review concerning the biology is presented in this paper. Besies a short description of the breed, it includes general aspects concern ing the laboratory breeds origin, their charac terization, evolutionary history and origin of common inbred st ains. The problem of laboratory use in researc h and issues concerning their reproduction particularitie a are also approached. The laboratory mouse has emerged as the preeminent model for human and animal research, building upon its well-established role i n biomedical sciences. Inbred, outbred, hybrid, knockout, or are ava ilable from many commercial sources. There are two common methods by which to characterize laboratory mice: genetics and microbial flora. Common genetic categories are random-bred which are managed to maintain genetic diversity by mating unrelated mice; Inbred which are managed to maintain genetic homozygosity by breeding siblings; F1 hybrid mice in which two inbred strains are crossbred for one generation; knockout mice in wh ich part of the genome has been removed or inactivated; transgenic mice in which specific genetic material has been introduced into the genome of another inbred mouse strain; mutant which are inbred that have developed genetic mutations. The microbial flora of can be used to group mi ce: Specific Pathogen Free Mice (SPF) are free from known bacterial, viral, an d parasitic mouse pathogens, as opposed to mice, which are not known to be free of pathogens. Most purchased at the University of Iowa are SPF but the standar d housing (i.e. conventional housing) cannot totally prevent the introduction of mouse pa thogens. To maintain the SPF microbial status of requires that animals be housed in m ore stringent conditions that prevent the introduction of rodent pathogens (i.e. barrier hous ing). This type of housing is available at the University of Iowa. Other less common microbial groups are axenic (i.e free from all microbial organisms) and gnotobiotic which have a known microbial flora. Evolutionary histrory Mus musculus Linn. the common house mouse, has been a member of man's immediate environment for many centuries. Along with other members of the order Rodentia, rats and constituting the family Muridae spread with man and his commerce from their origin in Asia to all parts of the world. Rodents are an extr emely diverse lineage with 3,000 species accounting for 40% of all mammalian species. Laboratory belong to the family Muridae (Old World mice) and the genus Mus . The commensal Mus musculus consists of four recognizable forms or morphotypes. These four morphotypes may be considered distinct species ( M. musculus, M. domesticus, M. castaneus, and M.bactrianus .) or subspecies of Mus