Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pregnancies. When deliberate steps are taken to end a pregnancy, it is called an induced abortion, or less frequently "induced miscarriage". The unmodified word abortion generally refers to an induced abortion. The reasons why women have abortions are diverse and vary across the world. Reasons include maternal health, an inability to afford a child, domestic violence, lack of support, feeling they are too young, wishing to complete education or advance a career, and not being able or willing to raise a child conceived as a result of rape or incest.

When properly done, induced abortion is one of the safest procedures in medicine.^: 1 In the United States, the risk of maternal mortality is 14 times lower after induced abortion than after childbirth. Unsafe abortions—those performed by people lacking the necessary skills, or in inadequately resourced settings—are responsible for between 5-13% of maternal deaths, especially in the developing world, though self-managed medication abortions are highly effective and safe. Public health data shows that making safe abortion legal and accessible reduces maternal deaths.

Modern methods use medication or surgery for abortions. The drug mifepristone in combination with prostaglandin appears to be as safe and effective as surgery during the first and second trimesters of pregnancy. 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 abortion. When performed legally and safely on a woman who desires it, induced abortions do 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 47,000 deaths and 5 million hospital admissions each year. 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".

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, 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.

Historically, abortions have been attempted using herbal medicines, sharp tools, forceful massage, or through other traditional methods. Abortion laws and cultural or religious views of abortions are different around the world. In some areas, abortion is legal only in specific cases such as rape, fetal defects, poverty, risk to a woman's health, or incest.

There is debate over the moral, ethical, and legal issues of abortion. 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 the legality of abortion often argue that it is part of a woman's right to make decisions about her own body. Others favor legal and accessible abortion as a public health measure.