Halloween is a holiday celebrated each year on October 31, and Halloween 2021  occurs on Sunday, October 31. The tradition originated with the ancient Celtic festival of Samhain, when people would light bonfires and wear costumes to ward off ghosts. In the eighth century, Pope Gregory III designated November 1 as a time to honor all saints. Soon, All Saints Day incorporated some of the traditions of Samhain. The evening before was known as All Hallows Eve, and later Halloween. Over time, Halloween evolved into a day of activities like trick-or-treating, carving jack-o-lanterns, festive gatherings, donning costumes and eating treats.

Halloween’s origins can be traced back to antiquity. Most point to Samhain, a Celtic festival which commemorated the end of the harvest season and the blurring of the physical and spirit worlds, as Halloween’s forebear. Over the ages, the holiday evolved, taking on Christian influences, European myth and American consumerism. Today, Halloween is celebrated with trick-or-treating, costumes, jack-o-lanterns and scary movies—all things which would likely be unrecognizable to those who took part in the holiday’s earliest forms.