Trick-or-treating traces back to a pre-Christian Celtic tradition called Samhain. The Celts, who lived 2,000 years ago in what is now Ireland, the UK and northern France, believed the dead returned to earth on the night of October 31. It is thought that people would gather to light bonfires, offer sacrifices and pay respects to spirits.

During these celebrations, villagers disguised themselves in costumes to drive away phantom ghosts, and laid food out to pacify unwelcome guests. The ritual later evolved to include dressing up as dark creatures and performing antics in exchange for food and drinks. 

Later on, when Christianity spread into Celtic lands, poor people would visit the houses of rich families and receive pastries in exchange for a promise to pray for the souls of the homeowners’ dead relatives. In Scotland and Ireland, rather than pledging to pray for the dead, they would sing a song, recite a poem, tell a joke or perform another sort of “trick” before collecting their treat, which typically consisted of fruits and sweets. 

As of now, trick-or-treating has a kid-centric focus. Is there a child who doesn’t like candy and costumes? Harvesting sweets by going door to door has become a custom observed nationwide in the US and in many other countries.