Halloween originated from the ancient Celtic festival of Samhain celebrated in Ireland, England, and Northern France over 2,000 years ago. It marked the transition between summer and winter and was associated with contacting the dead. People began wearing costumes to avoid being recognized as humans by ghosts on Halloween night. The traditions of wearing costumes and trick-or-treating were brought over to America by Irish immigrants fleeing the potato famine in the 1840s. Today, Halloween is celebrated with activities like carving jack-o-lanterns, decorating homes, wearing costumes, partying, and kids going trick-or-treating to collect candy.