The familiar customs of Halloween in the United States, from dressing up in costumes to trick-or-treating, from parties to ghost stories, from bobbing for apples to pranks, have origins hundreds, even thousands of years old.

Halloween is a holiday deeply linked to life and death. The history of Halloween is also a history of the religious, political, cultural, social, and even pop culture forces that have helped shape it into its modern incarnation.

The origin of Halloween lies in the Celtic holiday of Samhain Night, or "Oiche Samhain," a celebration of the dead as well as harvest and renewal. The Celts believed that on October 31, the last day of summer, the dead would return to mingle among the living. It was the day the dead transitioned to the underworld. The Druids, Celtic religious leaders, used the presence of spirits to aid in their predictions for the harvest. People lit bonfires to keep the ghosts from possessing them and to comfort the souls of the departed. The Celts doused their own hearth fires before the celebration, and afterwards, relit them from the sacred bonfires. To keep the dead from playing pranks, people gave the Druids food. This is likely part of the origin of trick or treating.

The Romans had conquered Celtic territory by 43 C.E., bringing their own traditions and religious beliefs with them. Feralia was a feast honoring the passing of the dead. There was also a feast to honor Pomona, goddess of fruit trees. Her symbol was the apple, which could be linked to the later tradition of bobbing for apples. In 609 C.E., Pope Boniface IV established a celebration of the Virgin Mary and the martyrs: All Saints Day. Originally this fell in May. In the eighth century, Pope Gregory II moved the date to November 1, but only within Rome. Pope Gregory IV extended that date to all Roman territories in 835 C.E. The Romans wanted to convert the pagans, and their strategy for doing so was to make the Catholic holidays fall on the same day as the pagan ones, which is also how Christmas, originally a pagan midwinter festival, got its date as well. Eventually the Druids had to go into hiding, as Roman missionaries sent back propaganda reports of devil-worship. To this day misconceptions still associate Halloween with evil.

The Mexican holiday the Day of the Dead, Los Dias de Los Muertos was originally an Aztec and Mayan tradition, a tribute to the dead that fell in July or August according to the Gregorian calendar. When the Spanish conquistadores arrived in the 15th century, they moved the date of the celebration of the dead to All Saints Eve and Day. The Mexican Day of the Dead celebrates the return of the Monarch butterflies who migrate to the US and Canada for the summer, and return to Mexico in autumn; the belief that butterflies carried the souls of the dead to the afterlife is an Aztec tradition. In Mexico, families observe the Day of the Dead by decorating the graves of deceased loved ones with flowers. They invite the spirits of the dead into their homes, creating an altar with flowers, pictures, food, and other things the dead person liked.

It is a celebration of children as well, a renewal of life. As in the American Halloween, sugary food plays a role; people eat sugar candy shaped into skulls and pan de muerto (bread of the dead).

Another origin of trick or treating may have been the European tradition of "souling." On November 2 , people would go to each other's homes and beg for "soul cakes," which were cakes baked with currants. This tradition carried over into English Halloween celebrations. In England, people celebrate Mischief Night on November 4, when pranks are carried out. Most notably, the English celebrate Guy Fawkes Day or Bonfire Night on November 5. Bonfire Night marks the foiling of a Catholic plot to blow up King James I and the Protestant aristocracy in the Parliament building in 1605. Guy Fawkes, one of the conspirators, was discovered and confessed the plot. People burn effigies of Guy Fawkes in what could be a subconscious throwback not only to the Celtic bonfires of Samhain, but additionally to the pagan harvest festival Lammas, which involved the burning in effigy of the harvest god (sometimes known as "John Barleycorn," immortalized in John Burns' poem of the same name).

October 31 also marks the date in 1517 when German scholar Martin Luther published his 95 points criticizing the Catholic church, which many felt had grown power hungry and decadent. This event kicked off the Protestant Reformation. In Catholic tradition, bells were rung on All Saints Eve to comfort souls in purgatory. During the Protestant Reformation, this and other Catholic practices were banned; in 1548 King Edward VI forbade the ringing of the bells on All Saints Eve.

In the seventeenth century, the Puritans, who objected to the power the monarchy had over religion, fled religious persecution to the New World. In New England, the celebration of All Saints Eve and Day, and the harvest celebration Samhain, was limited by the Puritan belief that holidays were decadent. However, in some areas of the American colonies, European customs and Native American ones began to mingle and formed the seeds of the modern American Halloween. Harvest celebration parties involved telling ghost stories, singing, and dancing. However, it was more a seasonal tribute to the harvest than Halloween as we know it now.

It was in fact the Irish and Scottish who brought Halloween to the United States. In the 1840's Irish immigrants fled the Potato Famine and came to America. The Scottish emigrated for similar reasons, seeking to escape from poverty and the lack of economic mobility in their home country. The Jack O' Lantern comes from an Irish story about a man named Jack who tricked Satan up into a tree, then carved a cross on it, trapping him there. In some accounts, Satan is cursed to wander between heaven and hell, welcome in neither, and the jack o' lantern is the lamp he carries, a hollow turnip with a candle inside. Scottish tradition involves Dirge Loaves, which are similar to the European soul cakes, pranking, and the carving of turnips. The Scottish harvest festival honors the return of the Cailleach Bhuer, the blue hag of winter. The last sheaf of corn from the harvest is dedicated to her.