Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. The unmodified word abortion generally refers to induced abortion, or deliberate actions to end a pregnancy. Abortion occurring without intervention is known as spontaneous abortion or "miscarriage", and occurs in roughly 30–40% of all pregnancies. Common reasons for inducing an abortion are birth-timing and limiting family size. Other reasons include maternal health, an inability to afford a child, domestic violence, lack of support, feelings of being too young, wishing to complete an education or advance a career, and not being able, or willing, to raise a child conceived as a result of rape or incest.

When done legally in industrialized societies, induced abortion is one of the safest procedures in medicine. Modern methods use medication or surgery for abortions. The drug mifepristone (aka RU-486) in combination with prostaglandin appears to be as safe and effective as surgery during the first and second trimesters of pregnancy. Self-managed medication abortion is highly effective and safe throughout the first trimester. The most common surgical technique involves dilating the cervix and using a suction device. Birth control, such as the pill or intrauterine devices, can be used immediately following an abortion. When performed legally and safely on a woman who desires it, an induced abortion does not increase the risk of long-term mental or physical problems. In contrast, unsafe abortions performed by unskilled individuals, with hazardous equipment, or in unsanitary facilities cause between 22,000 and 44,000 deaths and 6.9 million hospital admissions each year—responsible for between 5% and 13% of maternal deaths, especially in low income countries. The World Health Organization states that "access to legal, safe and comprehensive abortion care, including post-abortion care, is essential for the attainment of the highest possible level of sexual and reproductive health". Public health data show that making safe abortion legal and accessible reduces maternal deaths.

Around 73 million abortions are performed each year in the world, with about 45% done unsafely. Abortion rates changed little between 2003 and 2008, before which they decreased for at least two decades as access to family planning and birth control increased. As of 2018^[update], 37% of the world's women had access to legal abortions without limits as to reason. Countries that permit abortions have different limits on how late in pregnancy abortion is allowed. Abortion rates are similar between countries that restrict abortion and countries that broadly allow it, though this is partly because countries which restrict abortion tend to have higher unintended pregnancy rates.

Since 1973, there has been a global trend towards greater legal access to abortion, but there remains debate with regard to moral, religious, ethical, and legal issues. Those who oppose abortion often argue that an embryo or fetus is a person with a right to life, and thus equate abortion with murder. Those who support abortion's legality often argue that it is a woman's reproductive right. Others favor legal and accessible abortion as a public health measure. Abortion laws and views of the procedure are different around the world. In some countries abortion is legal and women have the right to make the choice about abortion. In some areas, abortion is legal only in specific cases such as rape, incest, fetal defects, poverty, and risk to a woman's health. Historically, abortions have been attempted using herbal medicines, sharp tools, forceful massage, or other traditional methods.

An induced abortion is a medical procedure to end a pregnancy. In present-day English, the term abortion, when used without further qualification, generally refers to induced abortion.

A pregnancy can be intentionally aborted in several ways. The abortion method depends upon the gestational age of the embryo or fetus, which gains mass as the pregnancy progresses. Abortion laws, regional availability, and the personal preference of the woman and her doctor may inform the woman's choice of a specific abortion procedure.

Abortions can be characterized as either therapeutic or elective. When an abortion is performed for medical reasons, the procedure is referred to as a therapeutic abortion. Medical reasons for therapeutic abortion include saving the life of the pregnant woman, preventing harm to the woman's physical or mental health, preventing the birth of a child who will have a significantly increased chance of mortality or morbidity, and reducing the number of fetuses to lessen health risks associated with multiple pregnancy. An abortion is referred to as elective or voluntary when it is performed at the request of the woman for non-medical reasons. Confusion sometimes arises over the term elective because "elective surgery" generally refers to all scheduled surgery, whether medically necessary or not.

About one in five pregnancies worldwide ends with an induced abortion. Most abortions result from unintended pregnancies. In the United Kingdom, 1 to 2% of abortions are done because of genetic problems in the fetus.