Experience with American college students, for the most part from Protestant Christian orientations, tells me that the popular conception of religion has two general features: Religion is a system (1) of beliefs and (2) of ethics, of right and wrong. This perception is not necessarily incorrect; but when it is applied to the Judaisms of the second temple period (520 b.c. to 70 a.d.) and to the biblical traditions that spring from them certain distortions can result. This chapter is devoted to one of the features of biblical religion that cannot simply be reduced to belief and ethics: the ritual matter of religious purity and impurity.