Enteric diseases of pigs and calves owing to Escherichia coli typically appear during the first few days (and weeks) of life. The so far recognized pathotypes of E. coli involved are the enterotoxic E. coli (ETEC), verotoxic E. coli (VTEC), enteropathogenic E. coli (EPEC), and necrotoxic E. coli (NTEC). The first step in the pathogenesis of all these types is to adhere to the intestinal microvilli with or without inducing morphological lesions and produce specific toxins acting locally on enterocytes and/or absorbed into the bloodstream. This action is assured by specific ligand (adhesins) and receptor interactions which are characteristic of the pathotypes involved and may vary according to the animal species. The host-adapted adhesin/receptor systems are targets of several preventive measures including vaccines, receptor blocking and breeding for genetic resistance. They also provide the basis for cross-species infections including zoonoses. Therefore they deserve the attention of epidemiologists, research scientists and technologists. Besides, they provide tools for increased understanding of molecular pathogenesis, and offer excellent models for comparative studies of different disease entities of enteric colibacillosis in humans.