The earliest recorded celebrators of the holiday were the Celts, who lived in what is now Ireland, Northern France, and the United Kingdom 2,000 years ago. Their New Years celebration was on November 1st and was a time when the line between the living and the dead was said to be blurred. The night before, on October 31st, was Samhain, pronounced sow-in the night when ghosts returned to the earth to cause trouble.

Celtic priests or Druids built large sacred bonfires on which animals and crops were burned in sacrifice to these spirits and also to Celtic deities. People also wore costumes during these celebrations, and told each others fortunes.

After the Celtic territory was conquered by the Romans, Celtic traditions were incorporated into a Roman holiday, celebrated in late October, known as Feralia, when the passing of the dead was commemorated. Another holiday, celebrated around the same time by the Romans was a day to honor Pomona, the Roman goddess of fruit and trees.

The influence of Christianity by the 800s resulted in the designation of November 1st as All Saints Day by Pope Boniface IV, in what some believe was an attempt by the Pope to replace the Celtic festival with a related, church approved holiday. This celebration was also known as All hallows, and the night before it, the traditional night of Samhain, began to be known as All Hallows Eve, or Halloween.

The influx of European immigrants to America meant a varied system of traditions and beliefs surrounding Halloween. In the New England colonies, celebrations were virtually forbidden, but in Maryland and other Southern colonies, these types of celebrations were fairly common, and included public gatherings when people would tell fortunes, dance, sing, and tell stories about the dead.

By the second half of the nineteenth century, new immigrants brought the tradition of going from house to house to ask for food and money, which is where the tradition of trick or treat originated. By the 1920s and 1930s, Halloween had become secularized and focused on community and less on ghosts and witchcraft. Between 1920 and 1950, trick or treating was also revived as a way to curb the vandalism that was prevalent on Halloween in many communities. Providing neighborhood children with treats was seen as an effective way to prevent this vandalism.

Today, Halloween is one of the most popular holidays of the year, incorporating ancient traditions of costumes and ghost stories with the more modern traditions.