Halloween is among the oldest traditions in the world as it touches on an essential element of the human condition: the relationship between the living and the dead. The observance evolved from ancient rituals marking the transition from summer to winter, thereby associating it with transformation, which is still a central theme of the holiday.

Every recorded civilization has created some form of ritual observance focused on what happens to people when they die, where they go, and how the living should best honor those who have passed or respond to the dead who seem unwilling or unable to move on. Countries around the world today celebrate Halloween in one form or another, from Mexico's Day of the Dead to China's Tomb Sweeping Day. The modern-day observance of Halloween in countries such as the United States and Canada – where this tradition is most popular – share in this ancient tradition, even though some aspects of the holiday are relatively recent developments, and can be traced back to the Celtic festival of Samhain.

​Halloween traditions in the West date back thousands of years to the festival of Samhain (pronounced `Soo-when', `So-ween' or `Saw-wen'), the Celtic New Year's festival. The name means “summer's end”, and the festival marked the close of the harvest season and the coming of winter. The Celts believed that the veil between the worlds of the living and the dead were thinnest at this time and so the dead could return and walk where they had before. Further, those who had died in the past year and who, for one reason or another, had not yet moved on, would do so at this time and could interact with the living.
THE OBSERVANCE OF SAMHAIN INCLUDED STOCKING UP SUPPLIES FOR THE WINTER, SLAUGHTERING CATTLE, AND DISPOSING OF THE BONES IN “BONE FIRES”.Very little is known of the rituals of ancient Samhain because the Church Christianized it – as with many pagan festivals – and what information is available comes from Irish monks who recorded the pre-Christian history of their people as well as other Christian scribes denigrating pagan rites. It seems, however, that the observance included stocking up supplies for the winter, slaughtering cattle, and disposing of the bones in “bone fires” which, in time, came to be known as bonfires. There were gatherings of communities for feasting and drinking while this was going on, but there was also the awareness of the “thin time” of the year and the possibility of otherworldly visitors showing up at the party.
Departed loved ones were expected – and welcomed – and the practice of setting out favorite foods for the dead may have originated as early as 2,000 years ago (though this is unclear), but many other kinds of spirits – some which never had human form – could also appear. Elves, fairies, the “wee folk”, sprites, and dark energies were just as likely to pay a visit as those one longed to see again one last time.
Further, there was a very good chance that the spirit of a person one may have wronged would also make an appearance. In order to deceive the spirits, people darkened their faces with ashes from the bonfires (a practice later known as “guising”), and this developed into wearing masks. A living person would recognize the spirit of a loved one and could then reveal themselves but otherwise remain safe from the unwanted attention of darker forces.