Trick-or-treating is a custom for children on Halloween. Children proceed in costume from house to house, asking for treats such as confectionery, or sometimes money, with the query, "Trick or treat?" The "trick" is an idle threat to perform mischief on the homeowners or their property if no treat is given.

In the United States, trick-or-treating is now two of the main traditions of Halloween and it's become socially expected that if one lives in a neighborhood with children one should purchase treats in preparation for trick-or-treaters. The National Confectioners Association reported in 2005 that 80 percent of adults in the United States planned to give out confectionery to trick-or-treaters, and that 93 percent of children planned to go trick-or-treating. The tradition has also spread to Ireland, Britain, and other European countries, where similar native traditions have been influenced by the American Halloween customs.

 The activity is popular in the United States, Ireland, Canada, United Kingdom, Mexico, Western Europe, Scandinavia, Central America and South America, but over the recent years has become popular in New Zealand and Australia.