Trick-or-treating or "Guising", is a customary practice for children on Halloween in many countries. Children in costumes travel from house to house in order to ask for treats such as candy (or, in some cultures, money) with the question "Trick or treat?". The "trick" is a (usually idle) threat to perform mischief on the homeowners or their property if no treat is given.

In North America, trick or treat has been a customary Halloween tradition since at least the late 1950s. Homeowners wishing to participate in it usually decorate their private entrance with plastic spiderwebs, paper skeletons and jack-o-lanterns. Some rather reluctant homeowners would simply leave the candy in pots on the porch, others might be more participative and would even ask an effort from the children in order to provide them with candy. In the more recent years, however, the practice has spread to almost any house within a neighborhood being visited by children, including senior residences and condominiums.

The tradition of going from door to door receiving food already existed in Great Britain and Ireland in the form of souling, where children and poor people would sing and say prayers for the dead in return for cakes. Guising — children disguised in costumes going from door to door for food and coins — also predates trick or treat, and is recorded in Scotland at Halloween in 1895, where masqueraders in disguise carrying lanterns made out of scooped out turnips, visit homes to be rewarded with cakes, fruit and money. While going from door to door in disguise has remained popular among Scots and Irish, the North American custom of saying "trick or treat" has recently become common. The activity is prevalent in the United States, Canada, United Kingdom, Republic of Ireland, Puerto Rico, and northwestern and central Mexico. In the latter, this practice is called calaverita (Spanish for "little skull"), and instead of "trick or treat", the children ask ¿me da mi calaverita? ("can you give me my little skull?"); where a calaverita is a small skull made of sugar or chocolate.