On October 31st, dozens of children dressed in costumes（节日服装）knock on their neighbors' doors and yell “Trick or Treat” when the door opens. Pirates and princesses, ghosts and popular heroes of the day all hold bags open to catch the candy or other goodies that the neighbors drop in. As they give each child a treat the neighbors exclaim over the costumes and try to guess who is under the masks.
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.
Today' school dances and neighborhood parties called “block parties” are popular among young and old alike. More and more adults celebrate Halloween. They dress up like historical or political figures and go to masquerade parties（化妆舞会）。 In larger cities, costumed children and their parents gather at shopping malls early in the evening. Stores and businesses give parties with games and treats for the children.Teenagers enjoy costume dances at their schools and the more outrageous the costume the better!
Certain pranks（恶作剧）such as soaping car windows and tipping over garbage cans are expected. But partying and pranks are not the only things that Halloweeners enjoy doing. Some collect money to buy food and medicine for needy children around the world.