The two Cryptophis species are moderate-sized (up to 1 m length) nocturnal venomous snakes of northern and eastern Australia. Examination of 600 museum specimens provided data on body sizes, sexual size dimorphism, reproductive cycles and food habits. Males attain larger body sizes than females in C. nigrescens, but not in C. pallidiceps. Both species are viviparous, with a mean litter size of four. Parturition occurs in late summer (Feb.-Mar.) in southern populations, but may be earlier in snakes from tropical areas. Relative clutch mass averaged 60% in captive C. nigrescens, and offspring averaged 152 mm SVL and 2.3 g mass at birth. Male combat was recorded in C. nigrescens. Both Cryptophis species feed on reptiles, especially scincid lizards (89% of all prey items found). A wide range of skinks is taken, but most are diurnally-active forms. Like many other Australian elapids, Cryptophis forage nocturnally for sleeping skinks. The absence of frogs from the diets of such elapids is a consistent but puzzling phemonenon. Relative eye size in Cryptophis is similar to that in other nocturnal elapids.