The commemoration of all the faithful departed is celebrated by the Church on November 2, or, if this be a Sunday or a solemnity, on November 3. The "Office of the Dead" must be recited by the clergy and all the Masses are to be of Requiem, except one of the current feast, where this is of obligation.

We read in Holy Scripture: “It is a holy and wholesome thought to pray for the dead, that they may be loosed from their sins.” II Maccabees 12:46

 
In the early days of Christianity the names of the departed brethren were entered in the diptychs. Later, in the sixth century, it was customary in Benedictine monasteries to hold a commemoration of the deceased members at Whitsuntide. In Spain there was such a day on Saturday before Sexagesima or before Pentecost, at the time of St. Isidore. In Germany there existed (according to the testimony of Widukind, Abbot of Corvey) a time-honored ceremony of praying to the dead on October 1st. This was accepted and sanctified by the Church. St. Odilo of Cluny ordered the commemoration of all the faithful departed to he held annually in the monasteries of his congregation.

All Souls Novena 

( say once a day for nine days, starting on October 25 until All Souls Day - November 2 )

O God, the Creater and Redeemer of all the faithful, grant to the souls of Thy servants and handmaids departed, the remission of all their sins; that through pious supplications they may obtain the pardon they have always desired. Who livest and reignest with God the Father in the unity of the Holy Ghost, God, world without end. Amen.