All Souls' Day is of double rank. Since 1917 it has a standing almost similar to a primary double of the first class of the Universal Church. Only if it falls on a Sunday is it transferred to the following Monday.
At Mattins the psalms are those used for Mattins of the Dead but the lessons are mostly proper to the day. At Lauds psalm 50, Miserere, is the first psalm and the rest from the Office of the Dead. The collect of the day is Fidelium.
The Little Hours have a special form. At Prime the Office begins after the silent recitation of the Pater, Ave and Credo with psalms 87, 27 & 31 without antiphons. Although the Miserere is sung at Lauds the displaced psalm is not transferred to Prime as on other days. At the reading of the Martyrology a special preamble is read, Hac die Commemoratio Omnium Fidelium Defunctorum..., before the announcement of the next day Tertio Nonas Novembris. Luna quintadecima etc. The psalms are sung either to the tone in directum or to a tone introduced with the Office of All Souls Day. Terce follows a similar, simplified, form and has psalms 37i, 37ii & 55. Sext psalms 69, 84 & 85 and None psalm 101 divided into three sections. The Office of the day ends with None.
In the Universal Church three Masses may be celebrated by every priest on this day. (The practice was first observed in Spain with an indult from Benedict XIV). This privilege was extended to the Universal Church by Benedict XV in 1915. The accepted practice of Collegiate churches is for the first Mass to be celebrated after Lauds, the second after Prime and the third after None. In all three Masses the sequence Dies irae is sung and the preface of the Dead is sung. Common practice is to have the Absolution of the Dead at a catafalque after the principal Mass.
Vespers are for the third day within the Octave of All Saints.
The above is in some ways a novelty. Prior to the 1911-13 reform the Office of the day was that of the second day within the Octave of All Saints. In addition to the Office of the day Vespers, Mattins and Lauds of the Dead were sung as they were on other days, namely the Mondays of Advent and Lent and the first 'free' day of each month. In parish churches a Requiem for the Dead was sung (the first of the current three) but in Cathedral and Collegiate churches two High Masses were sung one of the Octave of All Saints and a Requiem. The Office of the Dead was often celebrated as a 'Vigil' consisting of Vespers followed by Mattins and Lauds. This of course has an exact parallel in Slav-Byzantine parish worship where the aggregate of Vespers, Mattins & Lauds (and Prime) is celebrated on Saturday evenings and the eves of great feasts. With the 1911-13 reform the second day within the Octave disappeared and All Souls' Day was given a proper Office. Mattins of the Dead had a re-arrangement of lessons appointed for the day. Little Hours of the Dead were created based roughly on the Office of the Triduum. Compline, on the evening of All Saints after the double Vespers has psalms 122, 141 & 142 and the collect Propitiare quaesumus adapted from the secret of the Mass in die obitus. The other Little Hours have the psalmody described above.
In 'the liturgical books of 1962' the sequence Dies irae may be omitted in the second and third Masses when they are not sung. The last Gospel is omitted when the Absolution takes place. Vespers are of the Dead as these are no longer sung in their traditional place, after Vespers of the day yesterday. Compline of the Dead is transferred from yesterday to today.