This book chapter focus on the food-poisoning implications of Bacillus species. Before giving details on the food poisoning potential, the type of toxins and the method of detection, it briefly introduces the complex ecology and the identification challenges that characterize several Bacillus species. It uses use as an example the B. cereus group that shows a ‘bivalent face’ as far as its important impact on human activity ranging from very useful (worldwide used biocontrol agent B. thuringiensis) to even fatal pathogenic (B. anthracis and foodborne pathogen cereulide-producing B. cereus) species.