The protozoan parasite Cryptosporidium has gained better recognition over the last decade as an enteropathogen in a wide variety of host animals. Prior to 1975, infections were thought to occur infrequently and to be largely asymptomatic in nature. However, recent studies have revealed the organism to be more prevalent and pathogenic than previously thought. Infections producing clinical disease have been recorded in numerous host species including man, and the organism is now regarded as a newly-emergent zoonosis. This paper collates information currently available on the host range and specificity, life cycle and pathogenicity of the parasite and summarises the various techniques used to diagnose infections.