There is a comprehensive list in the Pentateuch of creatures that are regarded as unclean and therefore forbidden as food, or even to be touched (Lev. 11: 8); those animals that ruminate (chew the cud) but do not have cloven hooves, such as camels and hares, or vice versa in the case of pigs. Other unclean creatures include rats and mice, eels and crabs, insects (but not locusts), and some birds.

The attitude to unclean food caused bitter discussion in the early Church. Jewish Christians wished to continue the observance of the Law and demanded that Gentile converts should do so too. Paul resisted the demand, and denounced his opponents in his letter to the Galatians. The conflict is also reflected in the gospels (e.g. Mark 7: 19). Cf. Acts 10. See also clean and unclean.