Holy Week in the Christian year is the week immediately before Easter. The earliest catholic allusion to the custom of marking this week as a whole with special observances is to be found in the Apostolical Constitutions (v. 18, 19), dating from the latter half of the 1st century. In this text, abstinence from flesh is commanded for all the days, while for the Friday and Sunday an absolute fast is commanded. Dionysius Alexandrinus in his canonical epistle (AD 260), refers to the 91 fasting days implying that the observance of them had already become an established usage in his time.
In an ordinance attributed to Constantine, abstinence from public business was enforced for the seven days immediately preceding Easter Sunday, and also for the seven which followed it (Bright Week); the Codex Theodosianus, however, is explicit in ordering that all actions at law should cease, and the doors of all courts of law be closed during those 15 days (1. ii. tit. viii.). Of the particular days of the "great week" the earliest to emerge into special prominence was naturally Good Friday. Next came the Sabbatum Magnum ("Great Sabbath", i.e., Holy Saturday or Easter Eve) with its vigil, which in the early church was associated with an expectation that the second advent would occur on an Easter Sunday.
There are other Scriptures that refer to the traditions of the Early Church, most notably The Pilgrimage of Etheria (also known as The Pilgrimage of Egeria) which details the complete observance of Holy Week in the early church.
In the Orthodox Church, Great Lent ends on the Friday before Palm Sunday, though the faithful will continue fasting until Pascha (Easter). The day before Palm Sunday is called Lazarus Saturday and commemorates the resurrection of Lazarus. On Lazarus Saturday wine and oil are allowed (and, in the Russian tradition, caviar). Palm Sunday is considered one of the Great Feasts of the Lord, and is celebrated with fish, wine and oil. Because it is a Great Feast of the Lord, the normal Resurrectional elements of the Sunday All Night Vigil are omitted; however, these resurrectional elements are inserted into the Lazarus Saturday service with its theme of anticipating the Resurrection of Jesus.
Holy Week is referred to as "Great and Holy Week". Orthros (Matins) services for each day are held on the preceding evening. Thus, the Matins service of Great Monday is sung on Palm Sunday evening, and so on. This permits more of the faithful to attend, and shows that during Holy Week the times are out of joint—Matins ends up being served in the evening, and in some places Vespers is served in the morning.
Fasting during Great and Holy Week is very strict. Dairy products and meat products are strictly forbidden. On most days, no alcoholic beverages are permitted and no oil is used in the cooking. Friday and Saturday are observed as strict fast days, meaning that nothing should be eaten on those days. However, fasting is always adjusted to the needs of the individual, and those who are very young, ill or elderly are not expected to fast as strictly. Those who are able to, may receive the blessing of their spiritual father to observe an even stricter fast, whereby they eat only two meals that week: one on Wednesday night and one after Divine Liturgy on Thursday.
In Eastern Orthodoxy the day begins at sunset, so the first service of each day is Vespers, at which stichera are chanted commemorating the theme of the day.
The Orthros services of Palm Sunday are through Tuesday evenings are often referred to as the "Bridegroom Prayer", because of their theme of Christ as the Bridegroom of the Church, a theme expressed in the troparion that is solemnly chanted during them. On these days, an icon of the "Bridegroom" is placed on an analogion in the center of the temple, portraying Jesus wearing the purple robe of mockery and crowned with a crown of thorns (see Instruments of the Passion). The same theme is repeated in the exapostilarion, a hymn which occurs near the end of the service. These services follow much the same pattern as services on weekdays of Great Lent. The services are so laid out that the entire Psalter (with the exception of Kathisma XVII) is chanted on the first three days of Holy Week. The canon that is chanted on these days is a "Triode", i.e., composed of three odes instead of the usual nine odes (the canon of Holy and Great Tuesday is a "Diode", having only two odes).
Towards the end of the Tuesday evening Bridegroom service (Orthros for Great and Holy Wednesday), the Hymn of Kassiani is sung. The hymn, (written in the 9th century by Kassiani the Nun) tells of the woman who washed Christ's feet in the house of Simon the Pharisee. (Luke 7:36-50) Much of the hymn is written from the perspective of the sinful woman:
O Lord, the woman who had fallen into many sins, sensing Your Divinity, takes upon herself the duty of a myrrh-bearer. With lamentations she brings you myrrh in anticipation of your entombment. "Woe to me!" she cries, "for me night has become a frenzy of licentiousness, a dark and moonless love of sin. Receive the fountain of my tears, O You who gathers into clouds the waters of the sea. Incline unto me, unto the sighings of my heart, O You who bowed the heavens by your ineffable condescension. I will wash your immaculate feet with kisses and dry them again with the tresses of my hair; those very feet at whose sound Eve hid herself from in fear when she heard You walking in Paradise in the twilight of the day. As for the multitude of my sins and the depths of Your judgments, who can search them out, O Savior of souls, my Savior? Do not disdain me Your handmaiden, O You who are boundless in mercy."The Byzantine musical composition expresses the poetry so strongly that it leaves many people in a state of prayerful tears. The Hymn can last upwards of 25 minutes and is liturgically and musically a highpoint of the entire year.
On Great and Holy Monday, Tuesday and Wednesday the Divine Liturgy of the Presanctified Gifts is celebrated, at which the faithful may receive Holy Communion from the reserved Holy Mysteries. This service combines Vespers with a Communion Service. Each of these services has a reading from the Gospel which sets forth the theme for the day.
In many churches, especially Greek Orthodox, a service of Anointing (Holy Unction) is held on Wednesday evening, following the Presanctified Liturgy. This is in commemoration of the anointing of Jesus, and a preparation of the faithful to enter with Christ into his death and Resurrection. Those who wish to receive Holy Communion on Great and Holy Thursday, are encouraged to receive the Holy Mystery of Unction.
Orthros of Great and Holy Thursday does not follow the format of Great Lent (with the singular exception of chanting Alleluia in place of God is the Lord), but is celebrated as outside Lent, having a complete canon. Also, beginning at this service there will be no more reading of the psalter for the rest of Holy Week, with the exception of kathisma XVII at Orthros of Great and Holy Saturday.
Divine Liturgy of the Last Supper is held on the morning of Great and Holy Thursday, combining Vespers with the Liturgy of Saint Basil the Great. There is a custom among some churches to place a simple white linnen cloth over the Holy Table (altar) for this Liturgy, reminiscent of the Last Supper. In cathedrals and monasteries it is customary for the bishop or hegumen (abbot) to celebrate the Washing of Feet. When it is necessary for an autocephalous church to consecrate more chrysm the primate of that church will consecrate it at this Liturgy.
Great and Holy Thursday is the only day during Holy Week when those observing the strict tradition will eat a cooked meal, though they will not do so until after the dismissal of the Liturgy. At this meal wine and oil are permitted, but the faithful still abstain from meat and dairy products.
Matins of Great and Holy Friday is celebrated on the evening of Holy Thursday. During this service, twelve Matins Gospels are chanted, from which this service derives its name of "Matins of the Twelve Gospels". These Gospel lessons recount in chronological order the events from the Last Supper though the Crucifixion and burial of Jesus. At one point, when we reach the first Gospel which speaks of the Crucifixion, there is a custom for the priest to bring out a large cross with an icon the crucified Christ attached to it, and places it in the center of the nave for all the faithful to venerate. This cross will remain in the center of the church until the bringing out of the plashchanitza the next evening.
On Great and Holy Friday morning the Royal Hours are served. These are a solemn celebration of the Little Hours with added hymns and readings.
Vespers of Great and Holy Friday (Vespers of the Deposition from the Cross) is held in the morning or early afternoon of Great and Holy Friday. The figure of Christ is taken down from the Cross, and a richly-embroidered cloth icon called the Epitaphios (Church Slavonic: Plashchanitza) depicting Christ prepared for burial is laid in a "Tomb" decorated with flowers. At the end of the service all come forward to venerate the Epitaphios.
Compline of Great and Holy Friday contains a Canon of Lamentations of the Theotokos (Mother of God).
Matins of Great and Holy Saturday is held on Friday evening. The service is known as the "Orthros of Lamentations at the Tomb", because the majority of the service is composed of the clergy and faithful gathered around the tomb, chanting the "Lamentations" interspersed between the verses of Kathisma XVII (Psalm 118. At a certain point the priest sprinkles the tomb with rose petals and rose water. Near the end of the service, the Epitaphios is carried in a candlelit procession around the outside of the church as the faithful sing the Trisagion.
Vespers joined to the Divine Liturgy is served on Great and Holy Saturday morning. This is the Proti Anastasi (First Resurrection) service, commemorating the Harrowing of Hell. Just before the reading of the Gospel, the hangings and vestments and changed from dark lenten colors to white, and the entire mood of the service changes from mouring to joy. However, the faithful do not yet greet one another with the Paschal kiss, since the Resurrection has not yet been announced to the living.
If there are catechumens who are prepared for baptism they will usually be baptized and chrismated following the Liturgy of Great and Holy Saturday.
On Saturday night, the Paschal Vigil begins around 11:00 pm with the chanting of the Midnight Office. Afterwards, all of the lighting in the church is extinguished and all remain in silence and darkness until the stroke of midnight. Then, the priest lights a single candle from the eternal flame on the altar (which is never extinguished). The light is spread from person to person until everyone holds a lighted candle. Then a procession takes place circling around the outside of the church, recreating the journey of the Myrrh Bearers as they journeyed to the Tomb of Jesus on the first Easter morning. The procession stops in front of the closed doors of the church. The opening of these doors symbolized the "rolling away of the stone" from the tomb by the angel, and all enter the church joyfully singing the Troparion of Pascha. Paschal Orthros begins with an Ektenia (litany) and the chanting of the Paschal Canon. One of the highpoints is the sharing of the paschal kiss and the reading of the Hieratikon (Catechetical Homily of John Chrysostom) by the priest. The Divine Liturgy follows, and every Orthodox Christian is encouraged to confess and receive Holy Communion on this holiest day of the year. A breakfast usually follows, sometimes lasting till dawn. Slavs bring Easter baskets filled with eggs, meat, butter, and cheese—foods from which the faithful have abstained during Great Lent -- to be blessed by the priest which are then taken back home to be shared by family and friends with joy.
On the afternoon of Easter Day, a joyful service called "Agape Vespers" is celebrated During this service the Great Prokeimenon is chanted and a lesson from the Gospel (John 20:19-25) is read in as many different languages as possible, accompanied by the joyful ringing of bells.