Halloween is a holiday that has been celebrated for more than a thousand years. It originated as a religious observance and became increasingly secular over the centuries until its religious trappings all but disappeared. Halloween’s origins can be traced back to the ancient Celtic festival known as Samhain, which was held on November 1 in contemporary calendars. It was believed that on that day, the souls of the dead returned to their homes, so people dressed in costumes and lit bonfires to ward off spirits. In this way, popular Halloween tropes such as witches, ghosts, and goblins became associated with the holiday.

Over time, fall festivals marking the seasonal harvest incorporated Halloween elements, and Irish immigrants escaping the devastating Potato Famine brought with them many Halloween traditions that remain today. The custom of trick-or-treating, in which children dress up in costume and solicit treats from neighbors, became popular in the United States in the early 20th century as Irish and Scottish communities revived the Old World custom of “guising,” in which a person would dress in costume and tell a joke, recite a poem, or perform some other trick in exchange for a piece of fruit or other treat. By 1950, trick-or-treating for candy had become one of Halloween’s most popular activities.

Today, Halloween is considered a holiday for dress-up and fun, especially for children. It is one of the biggest holidays for candy sales in the United States, estimated to be worth billions of dollars annually. Halloween is celebrated on October 31, which is the eve of All Saints Day, a day in which Christians remember and honor the dead. The celebration marks the day before the Western Christian feast of All Saints and initiates the season of Allhallowtide, which lasts three days and concludes with All Souls’ Day.