Antinatalism or anti-natalism is the philosophical value judgment that procreation is unethical or unjustifiable. Antinatalists thus argue that humans should abstain from making children. Some antinatalists consider coming into existence to always be a serious harm. Their views are not necessarily limited only to humans but may encompass all sentient creatures, arguing that coming into existence is a serious harm for sentient beings in general.

There are various reasons why antinatalists believe human reproduction is problematic. The most common arguments for antinatalism include that life entails inevitable suffering, death is inevitable, and humans are born without their consent (that is to say, they cannot choose whether or not they come into existence). Additionally, although some people may turn out to be happy, this is not guaranteed, so to procreate is to gamble with another person's suffering. There is also an axiological asymmetry between good and bad things in life, such that coming into existence is always a harm, which is known as Benatar's asymmetry argument.

Antinatalism as a philosophical concept is to be distinguished from antinatalist policies employed by some countries (governmental population control measures). In antinatalist population policy, it is not always implied that coming into existence is a universal problem and is an ever-present harm to the one whose existence was started.

There exists a taxonomy that divides the so-called "antiprocreative" (at times called antinatalist) thought into four major branches: childfreeness, the Voluntary Human Extinction Movement (VHEMT), efilism (an ideology that advocates for extreme promortalism and forced extinction), and antinatalism itself. Only the latter one is philosophical antinatalism per se, meeting the definition of philosophical antinatalism and having no other features on top of that, whereas the first three items can only be deemed antinatalistic in the sense that they oppose the alleged duty to procreate.

The term antinatalism (in opposition to the term natalism, pronatalism or pro-natalism) was used probably for the first time by Théophile de Giraud in his book L'art de guillotiner les procréateurs: Manifeste anti-nataliste (2006). Masahiro Morioka defines antinatalism as "the thought that all human beings or all sentient beings should not be born." In scholarly and literary writings, various ethical arguments have been put forth in defense of antinatalism, probably the most prominent of which is the asymmetry argument, put forward by South African philosopher David Benatar. Robbert Zandbergen makes a distinction between so-called reactionary (or activist) antinatalism and its more philosophical, originary counterpart. While the former seeks to limit human reproduction locally and/or temporarily, the latter seeks to end it conclusively.

Antinatalist sentiments have existed for thousands of years. Some of the earliest surviving formulations of the idea that it would be better not to have been born can be found in ancient Greece. One example is from Sophocles's Oedipus at Colonus, written shortly before Sophocles's death in 406 BC:

Not to be born is, beyond all estimation, best; but when a man has seen the light of day, this is next best by far, that with utmost speed he should go back from where he came. For when he has seen youth go by, with its easy merry-making, what hard affliction is foreign to him, what suffering does he not know? Envy, factions, strife, battles, and murders. Last of all falls to his lot old age, blamed, weak, unsociable, friendless, wherein dwells every misery among miseries

From Gustave Flaubert, The Letters of Gustave Flaubert 1830–1857, 1846: