Halloween, name applied to the evening of October 31, preceding the Christian feast of Hallowmas, Allhallows, or All Saints' Day. The observances connected with Halloween are thought to have originated among the ancient Druids, who believed that on that evening, Saman, the lord of the dead, called forth hosts of evil spirits. The Druids customarily lit great fires on Halloween, apparently for the purpose of warding off all these spirits.

Among the ancient Celts, Halloween was the last evening of the year and was regarded as a propitious time for examining the portents of the future. The Celts also believed that the spirits of the dead revisited their earthly homes on that evening.

After the Romans conquered Britain, they added to Halloween features of the Roman harvest festival held on November 1 in honor of Pomona, goddess of the fruits of trees.

The Celtic tradition of lighting fires on Halloween survived until modern times in Scotland and Wales, and the concept of ghosts and witches is still common to all Halloween observances. Traces of the Roman harvest festival survive in the custom, prevalent in both the United States and Great Britain, of playing games involving fruit, such as ducking for apples in a tub of water. Of similar origin is the use of hollowed-out pumpkins carved to resemble grotesque faces and lit by candles placed inside.