Jewish law clearly prohibits male masturbation. This law is derived from the story of Onan (Gen. 38:8-10), who practiced coitus interruptus as a means of birth control to avoid fathering a child for his deceased brother. G-d killed Onan for this sin. Although Onan's act was not truly masturbation, Jewish law takes a very broad view of the acts prohibited by this passage, and forbids any act of ha-sh'cha'tat zerah (destruction of the seed), that is, ejaculation outside of the vagina. In fact, the prohibition is so strict that one passage in the Talmud states, "in the case of a man, the hand that reaches below the navel should be chopped off." (Niddah 13a)

The time of separation begins at the first sign of blood and ends in the evening of the woman's seventh "clean day." This separation lasts a minimum of 12 days. The Torah prohibits only sexual intercourse, but the rabbis broadened this prohibition, maintaining that a man may not even touch his wife or sleep in the same bed as her during this time. Weddings must be scheduled carefully, so that the woman is not in a state of niddah on her wedding night.

At the end of the period of niddah, as soon as possible after nightfall after the seventh clean day, the woman must immerse herself in a kosher mikvah, a ritual pool. The mikvah was traditionally used to cleanse a person of various forms of ritual impurity. Today, it is used primarily for this purpose and as part of the ritual of conversion, though in some communities observant men periodically immerse themselves for reasons of ritual purity.

It is important to note that the mikvah provides only ritual purification, not physical cleanliness; in fact, immersion in the mikvah is not valid unless the woman is thoroughly bathed before immersion. The mikvah is such an important part of traditional Jewish ritual life that traditionally a new community would build a mikvah before they would build a synagogue.