Shiga toxin-producing Escherichia coli (STEC) are pathogens responsible for human infections with a wide range of clinical manifestations. These range from mild watery diarrhea to hemorrhagic colitis and hemolytic uremic syndrome (HUS). HUS is the leading cause of acute kidney failure in young children. The main routes of STEC transmission to humans are the consumption of contaminated food and water, person-to-person transmission, and contact with carrier animals (particularly cattle). While not all STEC strains are pathogenic to humans, certain strains known as enterohemorrhagic E. coli (EHEC) are responsible for severe human infections. Five dominant EHEC serotypes have been identified to date in Europe (O157:H7, O26:H11, O103:H2, O111:H8, and O145:H28), but there are many other STEC serotypes that are more rarely implicated in human cases or outbreaks. This was the case very recently with serotype O104:H4, which caused two outbreaks in Germany and France. The purpose of this article is to define the properties of EHEC strains, with particular attention to the main serotypes responsible for human infections. This article will summarize the current state of knowledge regarding the various factors that may contribute to STEC virulence and their danger to humans. (R.A.)