Human sacrifice was practiced in many ancient cultures. Victims were ritually killed in a manner that was supposed to please or appease gods or spirits. On very rare occasions human sacrifices still occur today.
Reasons for human sacrifice include:
Human sacrifices were made in the Bronze Age Celtic religions in Europe, and in rituals related to worship of Norse gods (modern Ásatrú and Druidism do not condone such practices). However, because most of the information comes from outside sources (Greeks and Romans for Celts and medieval Christians for Norsemen) who may have had ulterior propaganda motives, modern historians consider them suspect.
Ancient Greeks practiced human sacrifice; references exist to sacrifice of maidens to Artemis.
According to Roman sources, Phoenicians and Carthaginians sacrificed infants to their gods; since Carthaginians were rivals to Roman power in the Mediterranean, this information is also sometimes considered suspect.
Early Romans practiced various forms of human sacrifice in their first centuries; from Etruscans (or, according to other sources, Sabellians), they adopted the original form of gladiatorial combat where the victim was slain in a ritual battle. During the early republic, criminals who had broken their oaths or defrauded others were sometimes "given to the gods" (that is, executed as a human sacrifice). Prisoners of war and Vestal virgins were buried alive as offerings to Manes and Dil Inferi (infernal gods). Archaeologists have found sacrificial victims buried in building foundations. Ordinarily, deceased Romans were cremated rather than buried.
Religious practices changed over the centuries. According to Pliny, human sacrifice was abolished by a senatorial decree in 97 BCE. Most of the rituals turned to animal sacrifice like taurobolium or became merely symbolic. A Roman general might bury a statue of his likeness to thank the gods for victory. Cicero refers to a sacrifice of rush puppets in the Vestal ritual that might have originally included sacrifice of old men. When the Roman Empire expanded, Romans stopped human sacrifices as barbarian.
Sacrifice in the Hebrew Bible
The Hebrew Bible generally condemns human sacrifice. In Genesis 22 there is a story about the near sacrifice of Isaac. In this story, God tests Abraham by asking him to present his son, Isaac, as a sacrifice on Mount Moriah. No reason is given within the text. Abraham agrees to this command without arguing. According to the text, God does not want Abraham to actually sacrifice his son; it states from the beginning that this is only a test. The story ends with God stopping Abraham at the last minute and making Isaac's sacrifice unnecessary by providing a goat, caught in some nearby bushes, to be sacrificed instead.
Some scholars have suggested this story's origin was a remembrance of an era when human sacrifice was abolished in favor of animal sacrifice.
Many passages in the Hebrew Bible state that human sacrifice was a great abomination; these practices were associated with the worship of foreign gods, and were forbidden. See, however, Judges 11:39, in which the Israelite leader Jephthah offered his daughter as a sacrifice in fulfilment of a vow. Although Jephthah's practice is not condoned (and is considered by rabbinic interpretation to be an epitome of a misguided and incorrect application of halakha), it shows that the practice did not die out completely within the world of the Israelites.
The practice of "banning" an enemy town in war by killing all its inhabitants - or, variously, only the people but not the animals; only the males; or only the adults - was commanded in several places. Where it was commanded, the act was subsequently considered a religious act pleasing to God. Some have argued this is a form of human sacrifice. King Saul was removed from the kingship for not rigorously carrying out this procedure when ordered by Samuel the prophet.
Jewish, Christian, Muslim, and modern historians' views on this subject can be found in the article on the near sacrifice of Isaac.
As written in Roman sources, Celtic Druids engaged extensively in human sacrifice. According to Julius Caesar, Gauls built wicker figures that were filled with living humans and then burned. It is known that druids at least supervised the sacrifices. During her rebellion against Roman occupation, Boudicca impaled any Romans she came across (such as in London) as offerings to gods. Some modern-day druidic scholars question the accuracy of these accounts.
Different gods reportedly required different kind of sacrifices. Worship of Attis included the selection of a young man who was treated as a king for a year and then sacrificed to ensure a good harvest. Victims meant for Esus were hanged, those meant for Taranis immolated and those for Teutates drowned. Some, like the Lindow Man, may have gone to their deaths willingly.
According to Norse mythology, Odin hanged himself from the world-tree Yggdrasil for nine nights to attain divine wisdom. Medieval Christian sources refer to Norsemen sacrificing prisoners by hanging them from trees, but the true extent of this behavior is unclear.
Norse warriors were sometimes buried with slave girls with the belief that the women would become their wives in Valhalla. A detailed eyewitness account of such a burial was given by Ahmad ibn Fadlan as part of his account of an embassy to the Volga Bulgars in 921. In his description of the funeral of a Rus′ notable, a slave girl volunteers to die with her master. After ten days of festivities, she is stabbed to death by an old woman (a sort of priestess who is referred to as 'Angel of Death') and burnt together with the deceased in his boat (see ship burial, Oseberg).
Adam von Bremen recorded human sacrifices to Odin in 11th century Sweden, at the Temple at Uppsala, a tradition which is confirmed by Gesta Danorum and the Norse sagas. According to the Ynglinga saga, king Domalde was sacrificed there in the hope to bring greater future harvests and general well-being to his people. The same saga also relates that Domalde's descendant king Aun sacrificed nine of his own sons to Odin in exchange for longer life, until the Swedes stopped him from sacrificing his last son, Egil. See also Blót.
The ancient Chinese are known to have made sacrifices of young men and women to river deities, and to have buried slaves alive with their owners upon death as part of a funeral service.
Some of the most famous forms of ancient human sacrifice were performed by various Pre-Columbian civilizations of Mesoamerica.
- The Aztecs were particularly noted for practicing human sacrifice on a large scale; an offering to Huitzilopochtli would be made to restore the blood he lost, as the sun was engaged in a daily battle. This would prevent the end of the world that could happen on each cycle of 52 years. The dedication of the great temple at Tenochtitlán was reported by the Aztecs as marked with the sacrifice of more than 84,000 prisioners, but this number may have been war propaganda by the Aztecs themselves (see the article on the Aztecs.)
- Sacrifices to Xipe Totec were bound to a post and shot full of arrows. The dead victim would be skinned and a priest would use the skin. Earth mother Teteoinnan required flayed female victims. Tlaloc would require weeping (sick) male children.
- Aztecs engaged in warfare - the so-called Flowery Wars - with the intent of capturing prisoners for sacrifice. There are multiple accounts of captured conquistadores being sacrificed during the wars of the Spanish conquest of Mexico, although only Bernal Diaz actually claimed to be a witness.
Tezcatlipoca required a voluntary sacrifice. Each year a youth was offered him as a victim. For a year he would be honored as a god on earth, and then he would be sacrified.
- According to Spanish sources, as well as frescoes and sculptures from the city of Tajin, the original form of the mesoamerican game ulama included sacrifice of the entire losing team. Tlachti , the Aztec version of the game, did not involve sacrifice.
Inca: A number of presumably sacrificial victims have been discovered in the Inca regions of South America. , the victims seem to have been left to die by cold, in the top of the mountains.
Hindu human sacrifice
See Sati, Purushamedha.
Modern human sacrifice
Human sacrifice still happens in some traditional religions, for example in muti killings in eastern Africa. Human sacrifice is no longer officially condoned in any country, and such cases are regarded as murder.
Some people in India are adherents of a religion called Tantrism (not to be confused with Tantric Buddhism); most either use animal sacrifice or symbolic effigies, but a very small percent of them still engage in real human sacrifice:
After a rash of similar killings in the area -- according to an unofficial tally in the English-language Hindustan Times, there have been 25 human sacrifices in western Uttar Pradesh in the last six months alone -- police have cracked down against tantriks, jailing four and forcing scores of others to close their businesses and pull their ads from newspapers and television stations. The killings and the stern official response have focused renewed attention on tantrism, an amalgam of mystical practices that grew out of Hinduism. (In India, case links mysticism, murder - John Lancaster, Washington Post, 11/29/2003)
In Western cultures no human sacrifice occurs beyond murders committed by serial killers or the largely unsubstantiated rumors of Satanic ritual abuse. Modern occultists consider such sacrifices unnecessary, or use them only in the symbolic form where the volunteer "sacrifice" is not actually killed. Christianity holds that the crucifixion of Jesus was history's most important sacrifice.
Some people have tried to extend the use of sacrifice-related terminology. A few writers have written that war--so often charged with religious and nationalistic symbols--is a form of human sacrifice. 
Historically prominent human sacrifices include:
Lindow Man in the United Kingdom
Tollund Man in Denmark (from the article: At first, Tollund Man was believed to be a rich man who had been ritually sacrificed, but recent analysis suggests that he may simply have been a criminal who was hanged and buried in the peat bog.)