Halloween originated from the ancient Celtic festival of Samhain, marking the end of the harvest season. Celts believed the night of October 31 was when the veil between the living and dead was thinnest and spirits of the deceased returned. To avoid being recognized by ghosts, people wore masks and costumes when leaving their homes at night. This tradition was brought to North America by Irish immigrants and evolved into the Halloween celebrations of today where children wear costumes and go trick-or-treating door-to-door asking for candy.