The control of microorganisms has always concerned food technologists. The fundamental biological similarities of bacteria, fungi etc. with humans can make “control” of food borne microorganisms rather than “elimination” a goal. Foodstuffs are ideal vehicles for microbial pathogens, degradative bacteria and fungi and the toxins they so often secrete. Heat, cold, reduced water activity and controlled atmospheres are largely outside the scope of this chapter, which concentrates on chemical techniques. Chemical preservatives inevitably have adverse effects on the physiology of micro-organisms so that possible adverse effects on consumers is a major issue. Sodium chloride has been a valued preservative since ancient times but nowadays its flavour is often as important as its effect on water activity. It is often used alongside nitrites and the biochemistry of nitrite's antimicrobial activity and interaction with muscle pigments is particularly complex. Smoking evolved from drying techniques but is now more important as a source of flavour. Sulfur dioxide, benzoates and other organic acids are most important for use with fruit based products. The antibiotics nisin and natamycin and ionising radiation have limited but valued applications. The chapter includes a detailed listing of the preservatives permitted as food additives in the EU, USA and elsewhere and concludes with a list of specialist books and review articles for further study.