Human cannibalism is the act or practice of humans eating the flesh or internal organs of other human beings. A person who practices cannibalism is called a cannibal. The meaning of "cannibalism" has been extended into zoology to describe an individual of a species consuming all or part of another individual of the same species as food, including sexual cannibalism.

Neanderthals are believed to have practiced cannibalism, and Neanderthals may have been eaten by anatomically modern humans. Cannibalism was also practiced in ancient Egypt, Roman Egypt and during famines in Egypt such as the great famine of 1199–1202. The Island Carib people of the Lesser Antilles, from whom the word "cannibalism" is derived, acquired a long-standing reputation as cannibals after their legends were recorded in the 17th century. Some controversy exists over the accuracy of these legends and the prevalence of actual cannibalism in the culture.

Cannibalism has been well documented in much of the world, including Fiji, the Amazon Basin, the Congo, and the Māori people of New Zealand. Cannibalism was also practiced in New Guinea and in parts of the Solomon Islands, and human flesh was sold at markets in some parts of Melanesia. Fiji was once known as the "Cannibal Isles".

Cannibalism has recently been both practiced and fiercely condemned in several wars, especially in Liberia and the Democratic Republic of the Congo. It was still practiced in Papua New Guinea as of 2012, for cultural reasons and in ritual as well as in war in various Melanesian tribes. Cannibalism has been said to test the bounds of cultural relativism because it challenges anthropologists "to define what is or is not beyond the pale of acceptable human behavior". Some scholars argue that no firm evidence exists that cannibalism has ever been a socially acceptable practice anywhere in the world, at any time in history, although this has been consistently debated against.

A form of cannibalism popular in early modern Europe was the consumption of body parts or blood for medical purposes. This practice was at its height during the 17th century, although as late as the second half of the 19th century some peasants attending an execution are recorded to have "rushed forward and scraped the ground with their hands that they might collect some of the bloody earth, which they subsequently crammed in their mouth, in hope that they might thus get rid of their disease."

Cannibalism has occasionally been practiced as a last resort by people suffering from famine, even in modern times. Famous examples include the ill-fated Donner Party (1846–47) and, more recently, the crash of Uruguayan Air Force Flight 571 (1972), after which some survivors ate the bodies of the dead. Additionally, there are cases of people suffering from mental illness engaging in cannibalism for sexual pleasure, such as Jeffrey Dahmer, Issei Sagawa, and Albert Fish. There is resistance to formally labeling cannibalism a mental disorder.