A litany (gr. Εκτενής ; sl. Ектения - Ektenija) is a prayerful sequence of supplications which are intoned by a deacon or priest in the name of all those praying. After each petition the choir or people sing, "Lord, have mercy," "Grant this, O Lord" (or in some translations, "Grant it, O Lord"), or "To Thee, O Lord" (or "To You, O Lord").
The Great Litany (Greek: Συναπτή μεγάλη/Synaptê Megalê; Slavonic: Ектенїѧ Великаѧ/Ekteniya Velikaya) --so called not only because of its length, but because of its importance, coming near the beginning of major services such as the Divine Liturgy, Matins, Vespers, Baptism, Great Blessing of Waters, etc. This ektenia is also called the Litany of Peace (Greek: Εἰρηνικά/Eirênika; Slavonic: Мирнаѧ Ектенїѧ/Mirnaya Ekteniya) because of the opening petition: "In peace, let us pray to the Lord."
The Small Litany (Greek: Αἴτησις/Aitêsis or Μικρὴ Συναπτή/Mikrê Synaptê; Slavonic: Ектенїѧ Малаѧ/Ektenia Malaya) is a shortened form of the Great Litany, consisting in only three petitions.
Litany of Supplication
The Litany of Supplication (Slavonic: Просительная ектения; Greek: Δέησις, Πληρωτικά), sometimes called Litany of Completion, is characterized by its first petition, "Let us complete our prayer unto the Lord," and by its petitions that end with "let us ask of the Lord," to which the faithful respond "Grant this, O Lord." The petitions beseech ("supplicate") the Lord for the spiritual well-being of the faithful. The initial petition may be modified to denote time of day (e.g. "Let us complete our evening prayer unto the Lord."), and therefore the Litany of Supplication may be called the "Evening Litany" or "Morning Litany," depending on the service in which it is said. In the Divine Liturgy, which is considered to be "outside of time," the Litany of Supplication does not denote a time of day.
Litany of Fervent Supplication
The Litany of Fervent Supplication (Slavonic: Ектенїѧ Сугубаѧ/Ekteniya Sugubaya)-- this litany is remarkable because of its fervency, indicated by the threefold response of the choir, "Lord, have mercy" (thrice). At the Divine Liturgy, this litany may also be augmented with special petitions, according to need as the presiding clergyman sees fit.
The Augmented Litany is so called because it consists of the petitions contained in the Litany of Fervent Supplication, augmented by two petitions at the beginning: "Let us say with all our soul and with all our mind, let us say:" and "O Lord Almighty, the God of our Fathers, we pray Thee, hearken and have mercy." The responses to these augmented petitions, unlike those taken from the Litany of Fervent Supplication, consist of a single "Lord have mercy," instead of three. The Augmented Litany may also be "augmented" with special petitions at times of need, such as for peace at times of war, for the health of a graevely-ill parishioner, the blessing of a new Marriage, etc.
Litany for the Departed
The Litany for the Departed is composed of entreaties to the Lord, that He might grant rest in the Heavenly Kingdom to the souls of the departed by forgiving them all their sins. It may be inserted into the Divine Liturgy, immediately following the Augmented Litany, especially at funerals and on Soul Saturdays, but also for the newly-departed, however never on a day of the Resurrection (i.e. Paschal-tide & Sundays).
Litany for the Catechumens
The Litany for the Catechumens (Slavonic: Ектенїѧ о Оглашенныхъ/Ekteniya o Oglashennuikh) contains petitions, offered by the Orthodox faithful, for the catechumens of the Church. These petitions ask the Lord to guide the catechumens in their journey toward "Illumination" in the Orthodox faith. This litany traditionally ended the part of the service which the catechumens were permitted to attend. The litany concludes with a dismissal of the catechumens, and (in older times) the closing of the doors of the temple to all but baptized members in good standing. The Litany for the Catechumens is found in the Divine Liturgy, and is immediately followed by the first Litany of the Faithful.
Litany of the Faithful
The first Litany of the Faithful dismisses the catechumens. At one time it was common for those who were not going to receive the Eucharist (among them the Catechumens) to move to the back of the church, or leave the building altogether, at the time of the Liturgy of the Faithful. The second Litany of the Faithful is usually abbreviated as a Little Litany when no deacon is serving, but normally contains several petitions from the Great Litany. The Litanies of the Faithful uniquely contain the exclamation, "Wisdom," just prior to their respective doxologies.
Litany of Thanksgiving
The Litany of Thanksgiving is a short litany that occurs after the hymn "Let our mouths be filled with Thy praise..." and before the prayer behind the ambon. It consists of three petitions and an the exclamation, "For Thou art our sanctification...", and is so named because the first petition includes the phrase "...let us worthily give thanks unto the Lord," and historically it is linked to the prayer of thanksgiving which the priest says immediately after communing himself.
The litia, which means a fervent or intensified prayer, most commonly refers to a part of Vespers that ends with the blessing of bread, wheat, wine, and oil for the strengthening of the faithful who continue worshiping during the Vigil. The litia is chanted at All-Night Vigils, consisting of several long petitions, mentioning the names of numerous saints, to which the people/choir responds with "Lord, have mercy" many times. In parish practice the litia is sometimes performed in the narthex of the church as the Church steps out of its blessed milieu and, in the character of the litia prayers, embraces all people. 
Special Litanies litanies occur only in particular services. These will usually be in the form of special petitions that are added to the Great Litany (such as at Baptism, or the special Kneeling Vespers at Pentecost), or unique litanies that occur in only one service (such as those at Molieben services or Holy Unction). At the Liturgy of the Presanctified Gifts many of the same litanies occur as during the Divine Liturgy, some of them being altered to conform to the needs of the Presanctified.
- Hapgood, Isabel F. (1922), Service Book of the Holy Orthodox-Catholic Apostolic Church (5th ed.), Englewood NJ: Antiochian Orthodox Christian Archdiocese (published 1975), pp. 13, 594
- []C. K. Zebrun Gen. Ed., Saints Commemorated in the Litiya Prayers, Department of Christian Education, Orthodox Church in America, 2009, pp4-5.