All Saints' Day is a celebration of all Christian saints, particularly those who have no special feast days of their own, in many Roman Catholic, Anglican and Protestant churches. In many western churches it is annually held November 1 and in many eastern churches it is celebrated on the first Sunday after Pentecost. It is also known as All Hallows Tide, All-Hallomas, or All Hallows' Day.

The vigil of the Feast (the eve) has grown up in the English speaking countries as a festival in itself, All Hallows Eve, or Halloween. While many consider Halloween pagan (and in many instances the celebrations are for many), as far as the Church is concerned the date is simply the eve of the feast of All Saints. Many customs of Halloween reflect the Christian belief that on the feast's vigils we mock evil, because as Christians, it has no real power over us. However, for some Halloween is used for evil purposes, in which many Christians dabble unknowingly. David Morrison explains the proper relationship between Christians and Halloween. Various customs have developed related to Halloween. In the Middle Ages, poor people in the community begged for "soul cakes," and upon receiving these doughnuts, they would agree to pray for departed souls. This is the root of our modern day "trick-or-treat." The custom of masks and costumes developed to mock evil and perhaps confuse the evil spirits by dressing as one of their own. Some Christians visit cemeteries on Halloween, not to practice evil, but to commemorate departed relatives and friends, with picnics and the last flowers of the year.

The day after All Saints day is called All Soul's Day, a day to remember and offer prayers up on behalf of all of the faithful departed. In many cultures it seems the two days share many customs. See the Oxford Dictionary of the Christian Church for more information.

Trick-or-treating is a customary celebration for children on Halloween. Children go in costume from house to house, asking for treats such as candy or sometimes money, with the question, "Trick or treat?" The word "trick" refers to a (mostly idle) "threat" to perform mischief on the homeowners or their property if no treat is given. In some parts of Scotland children still go guising. In this custom the child performs some sort of trick, i.e. sings a song or tells a ghost story, to earn their treats.

The practice of dressing up in costumes and begging door to door for treats on holidays dates back to the Middle Ages and includes Christmas wassailing. Trick-or-treating resembles the late medieval practice of souling, when poor folk would go door to door on Hallowmas, receiving food in return for prayers for the dead on All Souls' Day. It originated in Ireland and Britain,although similar practices for the souls of the dead were found as far south as Italy.Shakespeare mentions the practice in his comedy The Two Gentlemen of Verona, when Speed accuses his master of "puling like a beggar at Hallowmas."

Halloween costumes are traditionally modeled after supernatural figures such as monsters, ghosts, skeletons, witches, and devils. Over time, the costume selection extended to include popular characters from fiction, celebrities, and generic archetypes such as ninjas and princesses.

Dressing up in costumes and going "guising" was prevalent in Scotland at Halloween by the late 19th century. Costuming became popular for Halloween parties in the US in the early 20th century, as often for adults as for children. The first mass-produced Halloween costumes appeared in stores in the 1930s when trick-or-treating was becoming popular in the United States.

Halloween costume parties generally fall on, or around, 31 October, often falling on the Friday or Saturday prior to Halloween.

In Scotland and Ireland, Guising -- children disguised in costume going from door to door for food or coins-- is a traditional Halloween custom, 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.The practice of Guising at Halloween in North America is first recorded in 1911, where a newspaper in Kingston, Ontario reported children going "guising" around the neighborhood.