In the United States, Halloween is big business: The National Retail Federation estimates that Americans spent over 6 billion dollars on candy, costumes and ghoulish decor during the 2013 holiday. But what has become a commercial feast for candy producers and pumpkin farmers actually has its roots in an ancient Celtic festival, Samhain,
which marked the beginning of winter. The Celts believed that the night
before Samhain, spirits from the other world came and destroyed
vegetation with their breath, leaving the land barren for winter. People
would leave food and wine on their doorsteps to appease the spirits,
and wear masks when they left the house to blend in with them.
Eventually, the pagan tradition was co-opted by the Christian church in
the eighth century, and Samhain became All Saint's Day—or All Hallows. The night before became Hallows Eve (later Halloween for short).
-Smithsonian
