Not like All Saint's Day, Halloween is based around embracing scary things, particularly those involving death, the undead, "evil" magic, and mythical monsters. It is a liminal or threshold occasion, when the distinctions between the daylight world of reason and the spectral nightworld are blurred. Various traditions, and indeed even to this day people of different religious persuasions, celebrate "Halloween" in quite different ways. Certain customs long surviving in Ireland, were brought to the United States by Irish emigrants in the 19th century.

The origin of Halloween might be from Samhain, a Celtic holiday. The ancient Celts, which are people who lived in most of Western and Central Europe at 1000 BC, marked the end of harvest season and the beginning of winter by celebrating this holiday which took place each year at the night of October 31.  After the crops were harvested, Druids in Ireland and Britain would light fires and offer sacrifices of crops and animals. As they danced around the fires, the season of the sun passed and the season of darkness began. When the morning of November 1 arrived, the Druids would give an ember from their fires to each family who would then take them home to start new cooking fires. These fires were believed to keep the homes warm and free from evil spirits, as it was considered a time of year when the veils were thin between worlds. A three-day festival called Samhain (pronounced "sow-inn") followed. In Ireland it was believed to be the night on which the invisible "gates" between this world and the Other World were opened and free movement between both worlds was possible. In the Other World lived the immortal "Sidhe" (pronounced "shee"), the female members of whom were called beán sidhe or banshees.

Bonfires played a large part in the festivities and hundreds of fires are lit each year in Ireland on Halloween night. Villagers cast the bones of the slaughtered cattle upon the flames. The word "bonfire" is thought to derive from "bone fires." With the bonfire ablaze, the villagers extinguished all other fires. Each family then solemnly lit their hearth from the common flame, thus bonding the families of the village together.

Like most Celtic festivals, Samhain was celebrated on a number of levels. Materially speaking it was the time for gathering in food for the long winter months ahead, bringing people and their livestock in to their winter quarters. To be alone and missing at this dangerous time was to expose yourself and your spirit to the perils of imminent winter. In present times the importance of this part of the festival has diminished for most people.