Having children is a fundamental mitzvah, and large families are characteristic of the observant community. However, there are circumstances in which Jewish law permits or even mandates contraception, of various forms and at various times. Each couple should consult a rabbi for personal guidance in making a decision.
The Mitzvah of Having Children
Genesis 1:28, or according to some opinions, 9:7, is the source for the Torah commandment to "be fruitful and multiply". Technically, this commandment applies to men and not women. However, since today a man may have only one wife, she is an essential partner in enabling her husband to fulfill the commandment.
The Torah commandment is defined by halacha as having one son and one daughter who themselves reproduce. There also exists a rabbinic admonishment to continue to procreate even after fulfilling the quota mandated by the Torah. This is expounded from the verse in Ecclesiastes 11:6 "In the morning sow your seed, and in the evening do not desist." The exact definition and parameters of the rabbinic obligation are the subject of much discussion, and a couple should consult with their rabbi.
Reasons to Permit Contraception
Although there is a Torah commandment to have children, and although Jewish law strongly encourages families larger than the minimum size, contraception is permitted under certain circumstances. A woman whose life would be endangered by pregnancy or childbirth is required to use birth control, in accordance with the principle that all commandments (except for the prohibitions against adultery/incest, idolatry, and murder) are suspended where life is in danger. Other situations, including the woman's physical or emotional condition and the family's ability to cope, may also be grounds for allowing contraception. Some authorities permit spacing of births. Each couple should discuss their individual circumstances with a rabbinic authority.