Since the 800's November 1st is a religious holiday known as All Saints' Day(万圣节). The Mass that was said on this day was called Allhallowmas. The evening before became known as All Hakkiw e'en, or Halloween. Like some other American celebrations, its origins lie in both pre-Christian and Christian customs.

October 31 st was the eve of the Celtic(凯尔特人的)new year. The Celts were the ancestors of the present-day Irish, Welsh and Scottish people. On this day ghosts walked and mingled with the living, or so the Celts thought. The townspeople baked food all that day and when night fell they dressed up and tried to resemble the souls of the dead. Hoping that the ghosts would leave peacefully before midnight of the new year.

Much later, when Christianity spread throughout Ireland and October 31 was no longer the last day of the year, Halloween became a celebration mostly for children. "Ghosts" went from door to door asking for treats, or else a trick would be played on the owners of the house. When millions of Irish people immigrated to the United States in the 1840s the tradition came with them.