The liturgical year, intricate and majestic in its great cycles, overlapping and interlocking, is a yearly reminder of the birth, passion, death and resurrection of Christ; it represents the dynamic intersection of temporal and eternal, and lies at the basis of the organization of Christian life, the liturgy and the books in this exhibit. Given the weight of its message and the complexity of its calculation, it is small wonder that the liturgical calendar appears so baffling and is yet so fundamental.

A sacramentary from Mont-Saint-Michel in France, copied ca. 1060, with the full-page miniature of the Ascension, a moveable feast of the temporale.

 The two largest cycles are those called the temporale and the sanctorale. The Temporale (or Proper of Time) organizes the moveable feasts, those that are centered on Christ. Christmas, the birth of Christ, is the main moment in the temporale that is not moveable: it always occurs on 25 December. Advent, however, is variable in that it covers the four Sundays before Christmas. The other major feast in the temporale is Easter, the resurrection of Christ, which is observed on the first Sunday after the full moon that happens on or immediately after the spring equinox, which is taken as occurring on 21 March. This requires concordance among four time-measuring systems: the phases of the moon, the course of the sun, the yearly cycle (the last two for the spring equinox) and the days of the week; it allows for Easter to fall on any Sunday from 23 March to 26 April (i.e., 22 March and 25 April before the Gregorian reform of the calendar). Understandably, all the feasts that are dependent upon Easter are also variable, whether preceding (Lent, Quinquagesima, Sexagesima, Septuagesima, working backwards) or following (Ascension, Pentecost, Trinity, Corpus Christi, working forwards). As a consequence, the summer Sundays between Pentecost/Trinity and Advent may also vary in number since their termini at both ends move; the same is true of the Sundays between Epiphany and Lent with a moveable terminus at the end.

Since the saint's feast (on a fixed day) might coincide with a Sunday or any other moveable feast, a system for ranking the feasts evolved, in order to determine liturgical precedence and method of celebration: totum duplex, duplex, semiduplex, and so on form one system of classification. Calendars might instead specify the results of the classification, by the number of allotted readings at Matins (xii lectiones, ix lectiones, iii lectiones), by the level of the vestments (in cappis, in albis), or by the elaboration of ceremonial (cum candelis).

Hagiographic emphasis, especially if the saint is venerated only in one community, is of great help in localizing medieval liturgical manuscripts. The canonization date of a saint in the later Middle Ages can also be used to propose a terminus post quem for the production of the manuscript in which it is inscribed.

Morgan MS M.710: the so-called "Berthold Sacramentary," in fact a missal from Weingarten Abbey in Germany, ca. 1215-17, with extraordinary elegance and expense for the feast of St. Martin (11 November), one of the two patrons of the abbey.
A double-register full-page miniature with miracles of St. Martin, dividing his cloak and reviving the dead.	The concentric circle, inhabited by four men and the smaller swirl above it form the letter D, continued by the letters below, "-eus qui" as the beginning of the mass of St. Martin.

A ferial psalter from 15th century Germany whose calendar includes, in red ink, the feasts of Dominic "patris nostri" ranked as "totum duplex" (5 August) and Sebaldus (19 August) showing that the book was made for the Dominicans of Nurnberg.	A gradual from 15th century Italy with an inordinately large historiated initial of relatively unimportant saint: Helen, who found the True Cross (18 August). Presumably the book was made for a church with particular veneration of St. Helen.
An antiphonal from 16th century Spain, with the calendar leaf for November showing the feast of the relics of that church on 8 November, and the commemoration of the brothers of "our" order on 9 November.	A gradual printed in Venice in 1499-1500 with the Kyrie for feasts ranked as "major doubles."