The role of polyhydric alcohols in cryoprotection is probably the most extensively studied feature of insect cold hardiness. The importance of glycerol as a cryoprotectant was first recognized by R. W. Salt after he and others linked the presence of high levels of glycerol with winter hibernation, diapause, or freezing survival (Salt, 1957, 1959, 1961; Wyatt and Kalf, 1957; Chino, 1957). Over the last 30 years, literally hundreds of publications have described the occurrence of glycerol or other polyols in both freeze-tolerant and freeze-avoiding insects (for reviews, see Salt, 1961; Hansen, 1980; Ring, 1980; Sømme, 1982; Miller, 1982; Duman et al., 1982; Baust et al., 1982; Zachariassen, 1985; Lee et al., 1986; Storey and Storey, 1988). Glycerol is by far the most common cryoprotectant, but sorbitol, mannitol, ribitol, erythritol, threitol, and ethylene glycol also occur along with a selection of sugars, including trehalose, sucrose, glucose, and fructose (see Fig. 4.1) (Miller and Smith, 1975; Hayakawa and Chino, 1981; Sømme, 1982; Gehrken, 1984; Zachariassen, 1985; Hamilton et al., 1985; Storey and Storey, 1988). Glycerol contents that range as high as 25% of the fresh weight of the animal have been reported with polyol concentrations in excess of 2 M in the body fluids of many species (Salt, 1961; Ring, 1981; Zachariassen, 1985; Storey and Storey, 1988). The majority of species produce only a single polyol, but dual or even multiple component systems also occur, glycerol plus sorbitol being the most common pairing (Storey and Storey, 1988).