Halloween originated in Ireland and the broader Celtic world, with roots in the ancient festival of Samhain. Samhain marked the end of the harvest and the start of winter, and communities believed the boundary between the living and the dead was thinner on the night of October 31. This Irish/Celtic origin is widely cited as the historical source of Halloween customs that later spread to Britain, Ireland, and eventually to North America and other parts of the world through migration and cultural exchange. Modern Halloween traditions—costumes, bonfires, jack-o’-lanterns, and trick-or-treating—have been influenced by these Celtic practices and later developments, including Christian observances and popular culture.