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.

Halloween, celebrated on October 31, is a festival of costumes, candies, spooky tales, and ghostly decorations, enjoyed across many parts of the world. However, the origins of Halloween run much deeper than the playful and festive traditions associated with it today.

Samhain (/ˈsɑːwɪn/ SAH-win, /ˈsaʊɪn/ SOW-in, Irish: [ˈsˠəunʲ], Scottish Gaelic: [ˈs̪ãũ.ɪɲ]) or Sauin ( Manx: [ˈsoːɪnʲ]) is a Gaelic festival on 1 November marking the end of the harvest season and beginning of winter or the "darker half" of the year.

It came to the US from Europe, most notably from Ireland and Scotland, but it mostly died out across Europe right when it was picking up in the US. Most Halloween celebrated across the world is an American cultural export, including to much of Europe where it was revived with distinctly American traditions.