The pathogenic and spore-forming bacteria Bacillus cereus accounts for some of the most common foodborne poisonings, occurring under the forms of diarrheal and emetic syndromes due to a range of enterotoxins and to the cyclic peptide cereulide. Reports of Bacillus cereus outbreaks in Europe (including very severe emetic outbreaks) markedly increased in recent years. Spores of B. cereus are widely dispersed in the environment and contaminate any sort of foods. Assembly of spore structures is the result of a complex process and is strongly influenced by the environment of sporulation, with deep consequences on spore properties. With Clostridium botulinum and C. perfringens, B. cereus is a concern for mildly heat-processed foods because of spore resistance and the ability of many strains to multiply at refrigeration temperature. The phenotypic diversity of B. cereus strains has been established long ago. Several descriptions of the genetic structure of the whole group have been provided and now define genetic groups with specific phenotypic characters. With respect to food safety, these groups have different growth temperature profiles, and also differ by their involvement in foodborne poisoning incidents, production of toxins causing poisonings, resistance to heat, adaptation to low pH or to low aw, etc… The risk for consumers of B. cereus foodborne poisonings should be considered with respect to the type of strains present in foods.