Scotland, having a shared Gaelic culture and language with Ireland, has celebrated the festival of Samhain robustly for many centuries. The autumn festival is pre-christian Celtic in origin, and is known in Scottish Gaelic as Oidhche Shamhna, the “End of Summer”. During the fire festival, souls of the dead wander the earth and are free to return to the mortal world until dawn. Traditionally bonfires and lanterns, samhnag in Scottish Gaelic, would be lit to ward off the phantoms and evil spirits that emerge at midnight. The term Samhainn or Samhuinn is used for the harvest feast, and an t-Samhain is used for the entire month of November.

As in Ireland the exact customes and traditions celebrating Halloween from ancient times to pre-industrialised Scotland are lost and lack primary documentation to distinguish the ancient customs from the modern counterpart. The Witchcraft Act of 1735 contained a clause preventing the consumption of pork and pastry comestibles on Halloween, although in modern times such treats are a popular treat for children; the act was repealed in the 1950s. Scotland's National Bard Robert Burns portrayed the varied custom for children to dress up in costumes in his poem "Hallowe'en" (1785).

Halloween is seen when the division between the world of the living and the otherworld was blurred. Many of the traditional customs derive from ancient divination practices and ways of trying to predict the future. Most of the customs by the 18th century were methods for young people to search for their future husbands or wives. As Samhainn was originally a harvest festival, many of these strange practices are connected with food or the harvest—and fertility. One old custom associated with the Western Isles was to put two large nuts in the hearth of a peat fire. These were supposed to represent yourself and your intended spouse. If the nuts curled together when they warmed up then this was deemed to be a good omen, but if they jumped apart then it was time to look for another sweetheart. Islanders from Lewis traditionally poured ale into the sea in benefaction of a marine God called “Seonaidh” or “Shoney”on Celtic Samhain or Halloween, so that he will send seaweed to the shore to fertilise the fields for the coming year. Seonadh in Scottish Gaelic means sorcery, augury or Druidism, and it is possible the custom of Shonaidh is the direct link to an ancient form of Celtic god worship that has been Christianised. "Seonaidh", which is Gaelic "Johnny", may also be a reference to St. John, and an invocation to him.

Fire rituals were also important. Great bonfires were lit in a village, or by individual families, and when the fire died down, its ashes were used to form a circle. One stone for each member of the household is kept inside this circle near the circumference. If any stone is displaced or seems broken by next morning, then the person to whom that stone belongs is believed to die within a year. A similar rite in north Wales includes a great bonfire called Coel Coeth’ being built for each family on Halloween. Later, the members of the household throw a white stone in the ashes marked in their name. Next morning, all the stones are searched for and if any stone is missing, then the person who threw that stone, is believed to die before next Halloween.

In Scotland, folklore, including that of Halloween, revolves around the ancient Celtic belief in faeries: Sidhe or Sith in modern Gaelic. Children who ventured out carried a traditional lantern (samhnag) with a devil face carved into it, to frighten away the evil spirits. Such Halloween lanterns were made from a turnip or Neep in Lowland Scots, with a candle lit from a hollow inside. However, in modern times such lanterns use pumpkins, as in North American traditions. This is possibly because it is easier to carve a face in a pumpkin than in a turnip, and because of this, the practice of hollowing out pumpkins into jack-o-lanterns may have its roots in this practice.

Houses were also protected with the same candle lanterns. If the spirits got past the protection of the lanterns, the Scottish custom was to offer the spirits parcels of food to leave and spare the house another year. Children were also given added protection by disguising themselves as such creatures in order to blend in, and if they approached the door of a house, they were also given offerings of food—as Halloween is a harvest festival—to ward off the potential spirits that may lurk hidden among them. This is where the origin of the practice of Scottish guising—a word which comes from disguising, or travelling around in costume and is now included in the trick or treat tradition of North America.

In modern-day Scotland, this old tradition survives, chiefly by children going door to door guising in this manner, i.e., dressed in a disguise (often as a witch or ghost, monster or another supernatural being) and offering entertainment of various sorts. If the entertainment is enjoyed, the children are rewarded with gifts of sweets, fruits or money. There is no Scottish 'trick or treat' tradition as in North America; on the contrary, 'trick or treat' has its origins in the Scottish guising customs.

Popular games played on the holiday include "dooking" for apples (i.e., retrieving an apple from a bucket of water using only one's mouth). In places, the game has been replaced (because of fears of contracting saliva-borne illnesses in the water) by standing over the bowl holding a fork in one's mouth, and releasing it in an attempt to skewer an apple using only gravity. Another popular game is attempting to eat, while blindfolded, a treacle or jam coated scone on a piece of string hanging from the ceiling. Sometimes the blindfold is left out, because it is already difficult to eat the scone. In all versions, however, the participants cannot use their hands.

In 2007, Halloween festival organisers in Perthshire said they wanted to move away from US-style celebrations, in favor of more culturally accurate traditions. Plans include abandoning the use of pumpkins, and reinstating traditional activities such as a turnip lantern competition and "dooking (ducking) for apples".