Abstract Postharvest quarantine treatments using high temperatures have been developed for various commodities. There are a wide range of insect pests that are the target of these treatments. In order to make heat treatments effective against these pests, the effects of high temperatures on insect physiology must be understood. Insects, being poikilothermic, are particularly sensitive to heat. Nearly every system studied in insects has demonstrated sensitivity to heat. Studies on the effects of heat in insect metabolism demonstrate some adaptability to thermally challenging environments. Respiration, as to be expected, is also effected by heat, and as the body temperature of the insect increases, there are concomitant increases in both metabolism and respiration up to a critical thermal limit. The effects of heat on the nervous and endocrine systems is another area where elevated temperatures wreck havoc. Changes in behavior and development have been documented as resulting from heat treatments. Among the most studied responses of insects to heat is the elicitation of heat shock proteins. The impact of these proteins on thermotolerance are still being investigated. Models of thermal damage leading to the death of the insect are discussed as well as current studies in describing the events of thermal death.