In recent years, there has been a surge in the study of ritual impurity and its relationship to immorality (or, perhaps more accurately, prohibited activity) in biblical literature and early Judaism. Yet relatively scant attention has been paid to one of the most important topics pertaining to impurity—the menstrual laws of Leviticus (the laws of[niddah]) and their development in early Jewish texts. Theniddahlaws are uniquely important because they appear both in the context of ritual-impurity legislation (Leviticus 12 and Leviticus 15) and in the context of legislation concerning prohibited acts (Lev 18:19 and Lev 20:18). Or, to put it another way: biblical menstrual laws comprise both impurity and prohibition elements.