Enteroaggregative Escherichia coli heat-stable enterotoxin 1 (EAST1) is a small protein that was first detected more than a decade ago in an enteroaggregative E. coli (EAEC) strain isolated from the stools of a diarrheic child. The EAST1 gene, astA, is not solely present in EAEC, but also in other categories of diarrheagenic E. coli. Strains expressing EAST1 have been shown to induce diarrhea principally in humans, although they have also been associated with piglets and calves. EAST1 toxin has been proposed as a virulence factor implicated in the mechanism of pathogenesis of EAEC and could play a role in the pathogenicity of other enteropathogens as well. This toxin is often compared to E. coli STa enterotoxin because they share some physical and mechanistic similarities. This review summarizes the various observations on EAST1 since its discovery.