Human sacrifice is the act of killing one or more humans as part of a ritual, which is usually intended to please or appease gods, a human ruler, public or jurisdictional demands for justice by capital punishment, an authoritative/priestly figure, spirits of dead ancestors or as a retainer sacrifice, wherein a monarch's servants are killed in order for them to continue to serve their master in the next life. Closely related practices found in some tribal societies are cannibalism and headhunting. Human sacrifice is also known as ritual murder.

Human sacrifice was practiced in many societies, beginning in prehistoric times. By the Iron Age (1st millennium BCE), with the associated developments in religion (the Axial Age), human sacrifice was becoming less common throughout Africa, Europe, and Asia. During classical antiquity, it came to be looked down upon as barbaric. In the Americas, however, human sacrifice continued to be practiced, by some, to varying degrees until the European colonization of the Americas. Today, human sacrifice has become extremely rare.

Modern secular laws treat human sacrifices as murder. Most major religions in the modern day condemn the practice.

Human sacrifice has been practiced on a number of different occasions and in many different cultures. The various rationalisations behind human sacrifice are the same that motivate religious sacrifice in general. Human sacrifice is typically intended to bring good fortune and to pacify the gods, for example in the context of the dedication of a completed building like a temple or bridge. Fertility was another common theme in ancient religious sacrifices, such as sacrifices to the Aztec god of agriculture Xipe Totec.

In ancient Japan, legends talk about hitobashira ("human pillar"), in which people were buried alive at the base of or near some constructions to protect the buildings against disasters or enemy attacks, and almost identical accounts appear in the Balkans (The Building of Skadar and Bridge of Arta).^{[citation needed]}

For the re-consecration of the Great Pyramid of Tenochtitlan in 1487, the Aztecs reported that they killed about 80,400 prisoners over the course of four days. According to Ross Hassig, author of Aztec Warfare, "between 10,000 and 80,400 persons" were sacrificed in the ceremony.

Human sacrifice can also have the intention of winning the gods' favor in warfare. In Homeric legend, Iphigeneia was to be sacrificed by her father Agamemnon to appease Artemis so she would allow the Greeks to wage the Trojan War.

In some notions of an afterlife, the deceased will benefit from victims killed at his funeral. Mongols, Scythians, early Egyptians and various Mesoamerican chiefs could take most of their household, including servants and concubines, with them to the next world. This is sometimes called a "retainer sacrifice", as the leader's retainers would be sacrificed along with their master, so that they could continue to serve him in the afterlife.^{[citation needed]}