All Souls' Day is observed on November 2nd or the 3rd if the 2nd falls on a Sunday and is right after All Saints' Day. It is observed by the Roman Catholics. The Abbot of Cluny, Odilo, established All Souls' Day in the eleventh century and ordered that it would follow All Saints' Day to change attention from the martyrs and saints to those stuck in purgatory. Three requiem masses are celebrated on All Souls' Day: one for the celebrant, one for the departed, and one for the Pope. It is similar to the pagan holiday, Festival of the Dead, and is sometimes called the "Day of the Dead."

Catholics believe that when a person dies, he spends time in purgatory where he is cleansed from sin through suffering. Prayer and good works of those who are still alive will shorten a person's stay in purgatory. All Saints' Day remembers the martyrs and saints who have died; All Souls' Day remembers those who are in purgatory.