Escherichia coli O157 was recognised as a human pathogen in the late 1970s, its public health significance being recognised in 1982 when it was implicated in a large outbreak of infection associated with a fast-food restaurant in North America. Incidence of infection in the population is relatively low compared to other enteric pathogens; however, this organism causes a spectrum of disease increasing in severity from a mild diarrhoeal illness to haemorrhagic colitis, haemolytic uraemic syndrome (HUS) and, in some cases, death. Production of verocytotoxin and intimin, and the presence of a 60 mDa plasmid are thought to be important virulence factors; however, many currently unidentified factors may also contribute. The infectious dose of this organism is low and reports of food-borne, water-borne and person-to-person transmission have occurred, including several laboratory-acquired infections. Techniques for isolation, identification and confirmation of these organisms, based on cultural, immunological and molecular detection, are described. Additionally, schemes have been developed to type these organisms for epidemiological investigation, and the roles of phage typing and genotyping are discussed. These enable identification of sources and the introduction of intervention strategies for prevention of spread in the community.