On Halloween, which is celebrated on October 31st in Britain and the U.S., people dress up in costumes like witches, vampires, and monsters. Children go trick-or-treating, visiting neighbors and asking for candy while carrying jack-o'-lanterns - hollowed out pumpkins with candles inside. The origins of Halloween come from the ancient Celtic festival of Samhain, celebrated by the Celts in Ireland, the UK, and France to mark the end of the harvest season and the beginning of winter.