The Pentecostarion (, ; , , literally "Flowery Triodon"; ) is the liturgical book used by the Eastern Orthodox and Byzantine Catholic churches during the Paschal Season which extends from Pascha (Easter) to the Sunday following All Saints Sunday (i.e., the Second Sunday After Pentecost).
The name means the Book of the "Fifty Days", referring to the period of time from Pascha to Pentecost. In Greek, it is also sometimes called the Joyful Pentecostarion (, ). In English, it is sometimes called the Paschal Triodion. The name "Pentecostarion" is also applied to the liturgical season covered by the book.
The Pentecostarion is part of the Paschal cycle or "Moveable Cycle" of the ecclesiastical year. This cycle is dependent upon the date of Pascha and continued throughout the coming year until the next Pascha.
Pascha (Easter) is the most important feast of the entire year, outranking by far all others. Each week of the Pentecostarion is named after the Gospel lesson which is read on the Sunday which begins it; for instance, the week that follows Thomas Sunday is referred to as Thomas Week. During the liturgical season of the Pentecostarion, the Gospel of John is read in full, as is the Acts of the Apostles. Both of these books were chosen because of their instructive content. Pascha (Easter) is the traditional time for baptizing new converts to the faith. So, just as Great Lent, with its liturgical book, the Triodion, was the final period of preparation for the catechumens before their baptism, so the time of the Pentecostarion is the time of initiation into the Sacred Mysteries of the Christian religion for the "Newly Illumined" (i.e., the newly baptized).
The two Sacred Mysteries of baptism and chrismation are reflected in the two feasts which mark the beginning and ending points of the Pentecostarion: Pascha and Pentecost. Baptism is naturally tied to the Resurrection, according to the Apostle Paul. Chrismation, the reception of the Gifts of the Holy Spirit is naturally reflected in Pentecost. Because of this, the imagery of water figures prominently in the hymns of the Pentecostarion.
The services of the Pentecostarion begin during the Paschal Vigil starting at the stroke of midnight on Easter Sunday. The service for Pascha is radically different from the services of any other time of the year. Throughout the course of the Pentecostarion, they gradually return to normal (see Canonical hours and Divine Liturgy).
Afterfeast of Pascha
The Afterfeast of Pascha lasts for 40 days, beginning on the Sunday of Pascha and concluding with the Apodosis ("leave-taking") of Pascha on the day before the Ascension of the Lord.
Bright Week
The seven days beginning on the Sunday of Pascha are referred to as "Bright Week" or "Renewal Week". On these days the services are completely different that the rest of the year. Everything is chanted rather than being simply read. Most of the services are much shorter than usual. Even the Divine Liturgy, which normally has little variation in it, has a number of changes which are particular to the Paschal celebration. The Little Hours are chanted in a special format known as the Paschal Hours. The reading of the Psalter, which normally forms a major portion of all of the Daily Offices, is completely omitted.
In the temple (church building), the Holy Doors on the iconostasis are left open for the entire week, symbolizing the open Tomb of Christ, and the Epitaphion (shroud) is visible on the Holy Table (altar), representing the burial cloths () which, according to Christian tradition, bore witness to the Resurrection of Jesus.
The Paschal Artos (, "leavened loaf") is a loaf of risen bread bearing an icon of the Resurrection on it, which is blessed near the end the Paschal Vigil. It is then placed either near the Icon of Christ on the iconostasis or in the nave of the church. The Artos represents the physical presence of Jesus after his Resurrection, and is venerated by the faithful when they enter or leave the temple as a way of greeting the Resurrected Christ.
At the end of either Matins or the Divine Liturgy, there is often a crucession (procession headed by the cross), during which the Paschal Canon is chanted, and the priest blesses with holy water.
Unique to Vespers and Matins during Bright Week is the use of the singing of the verse of Psalm 67 responsorially with the Paschal Troparion in place of the usual Psalm 104 at Vespers and the Hexapsalms at Matins.