Abortion may be defined as the spontaneous or induced expulsion of an embryo or fetus before it is viable or can survive on its own. Complications may occur with the development of a fetus during pregnancy. These complications may be due to various genetic, medical, or hormonal problems, and the result is termination of the pregnancy. This termination of pregnancy is called a miscarriage or a spontaneous abortion. In contrast to a spontaneous abortion, an induced abortion involves a decision to terminate a pregnancy by medical procedures.

Abortions are a critical facet of women's health. Each year, more than 6 million American women become pregnant, and more than half of these pregnancies are unintended. Of these unintended pregnancies, approximately 1.6 million terminate their unintended pregnancy through abortion.

Induced abortion has been both controversial and widely practiced for centuries. The history and politics of abortion is long and complex. Anthropological studies have revealed that abortion practice was widespread in ancient and preindustrial societies. In the Western World before Christianity, Greeks and Romans considered abortion acceptable during the early stages of pregnancy. A prescription for abortion has been found in the Hippocratic oath taken by Greek physicians. Until the late 1800s, women healers in Western Europe and the United States provided abortions and trained other women to do so, without legal prohibitions. The movement to establish abortion as both criminal and sinful was led by male physicians as part of a crusade from 1860 to 1880 to outlaw all forms of contraception. By 1965, all 50 states had passed legislation prohibiting abortion during all stages of pregnancy. The issue of equity entered abortion public policy consideration. Women with greater personal financial resources were able to arrange for safer, more "legal" abortions by traveling to less rigid jurisdictions or by persuading physicians to make therapeutic exceptions. Women with fewer financial resources were more likely to suffer from unsafe abortions and incompetent abortionists. Legal prohibition did not have the effect of reducing the incidence of abortions. Estimates of the annual number of illegal abortions in the 1950s and 1960s ranged from 2000,000 to 1.2 million.

In the early 1970s, legal challenges were increasingly mounted against any prohibition of a woman's ability to obtain an abortion. Abortion was legalized in the United States on January 22, 1973, through the landmark Supreme Court decision Roe v. Wade. This decision declared unconstitutional all state laws that prohibited or restricted abortion during the first trimester of pregnancy. The decision stated that the "right of privacy … founded on the Fourteenth Amendment's concept of personal liberty … is broad enough to encompass a woman's decision whether or not to terminate her pregnancy." The ruling also limited state interventions in second-trimester abortions and left the issue of third-trimester abortions up to each individual state.

The Roe v. Wade decision was immediately greeted with opposition. The "right-to-life" movement was originally a creation of The Family Life division of the National Conference of Catholic Bishops (NCCB), the directive body of the Catholic Church in the United States. Immediately following the Supreme Court decision of Roe v. Wade, the NCCB Pro-Life Affairs committee declared that it would not accept the Court's judgment and called for a major legal and educational battle against abortion rights, was formed in 1973 to support the Supreme Court decision and preserve the right of women, regardless of income, to have their choice of legal abortions.

A number of states in 1974 and 1975 instituted restrictions in the ruling by enacting laws requiring teens seeking abortion to have parental permission. This legislation, however, was declared unconstitutional by the Supreme Court in 1976. The decision stated that a minor should have free access to sex-related health care and that a third party such as a parent could not veto a decision made by the physician and the patient to terminate the patient's pregnancy.

In 1976, the Hyde Amendment was introduced and passed in Congress. This legislation was a major setback to the abortion movement because it banned Medicaid funding for abortion unless a woman's life was in danger. It has been argued that this amendment disproportionately affected low-income women. A temporary injunction stalled the Hyde Amendment for a year. Meanwhile in June 1977, the Supreme Court ruled that states did not have to fund what they considered "medically unnecessary" abortions. In December 1977, a compromise version of the amendment added exceptions for promptly reported rape and incest cases in which two physicians would testify that the woman's health would be seriously impaired by maintaining the pregnancy. Many groups fought against the Hyde Amendment, but the final ruling of the Supreme Court upheld it in the 1980 Harris v. McRae decision. Although the Supreme Court reaffirmed the central holding of Roe v. Wade in 1986, a newly constituted court agreed to hear Webster v. Reproductive Health Services in 1989. The supreme Court decision on the Webster case returned to the states the authority to limit a woman's right to a legal abortion. The saga continues into the 1990s.