Both the Feast of All Saints and the Feast of All Souls are celebrated at the beginning of November.
All Saints' Day is also known as The Solemnity of All Saints. All Saints' Day is the day when all known and unknown saints are honored. It originated with the Christian tradition of the martyrdom of saints and was celebrated on the anniversary and place of martyrdom for each saint. As martyrdoms increased during the persecutions of the Roman Empire, it was not possible to celebrate a separate feast for each martyr. Therefore, many dioceses established a common feast day so that all martyrs were honored properly. Pope Gregory III (731-741) instituted the current date of All Saints' Day, November 1st, when he consecrated a chapel in Rome to all martyrs at St. Peter's Basilica, and the celebration was extended to the entire Church.
All Souls' Day is when we celebrate all those who have died. Pope Benedict XV (1914-22) made clear the importance of All Souls' Day when he allowed priests to celebrate three Masses on All Souls' Day. The three Masses were for the faithful departed, the priest's intentions, and the Holy Father's intentions. All Souls' Day was originally celebrated during the Easter season around Pentecost Sunday. Between the years 998 and 1030, St. Odilo of Cluny made a decree that All Souls' Day should be celebrated on November 2nd in all of his Benedictine monasteries. The celebration of All Souls' Day soon spread to the entire Catholic Church.