Unlike in Western Christianity, where individual religious orders and societies arose, each with its own profession rites, in the Eastern Orthodox Church, there is only one type of monasticism. The profession of monastics is known as Tonsure (referring to the ritual cutting of the monastic's hair which takes place during the service) and was, at one time, considered to be a Sacred Mystery (Sacrament). The Rite of Tonsure is printed in the Euchologion (Church Slavonic: Trebnik), the same book as the other Sacred Mysteries and services performed according to need, e.g., funerals, blessings, exorcisms, etc.
The monastic habit is the same throughout the Eastern Church (with certain slight regional variations), and it is the same for both monks and nuns. Each successive grade is given a portion of the habit, the full habit being worn only by those in the highest grade, known for that reason as the "Great Schema", or "Great Habit". One is free to enter any monastery of one's choice; but after being accepted by the abbot (or abbess) and making vows, one may not move from place to place without the blessing of one's ecclesiastical superior.
One becomes a monk or nun by being tonsured, a rite which only a priest can perform. This is typically done by the abbot. The priest tonsuring a monk or nun must himself be tonsured into the same or greater degree of monasticism that he is tonsuring into. In other words, only a hieromonk who has been tonsured into the Great Schema may himself tonsure a Schemamonk. A bishop, however, may tonsure into any rank, regardless of his own; also, on rare occasion, a bishop will allow a priest to tonsure a monk or nun into any rank.
Eastern Orthodox monks are addressed as "Father", as are priests and deacons in the Orthodox Church; but when conversing among themselves, monks in some places may address one another as "Brother". Novices are most often referred to as "Brother", although some places, e.g., on Mount Athos, novices are addressed as "Father". Among the Greeks, old monks are often called Gheronda, or "Elder", out of respect for their dedication. In the Slavic tradition, the title of Elder (Church Slavonic: старецъ, Starets) is normally reserved for those who are of an advanced spiritual life, and who serve as guides for others.
Nuns who have been tonsured to the Stavrophore or higher are addressed as "Mother". Novice and Rassophore nuns are addressed as "Sister". Nuns live identical ascetic lives to their male counterparts and are therefore also called monachai (the feminine plural of monachos), and their community is likewise called a monastery.
Monks who have been ordained to the priesthood are called hieromonks (priest-monks); monks who have been ordained to the diaconate are called hierodeacons (deacon-monks). A Schemamonk who is a priest is called a Hieroschemamonk. Most monks are not ordained; a community will normally only present as many candidates for ordination to the bishop as the liturgical needs of the community require. Bishops are required by the sacred canons of the Orthodox Church to be chosen from among the monastic clergy.
Today, the most important centres of Christian Orthodox monasticism are Saint Catherine's Monastery in the Sinai Peninsula (Egypt), Meteora at Thessaly in Greece, Mount Athos in Greek Macedonia, Mar Saba in the Bethlehem Governorate of the West Bank, and the Monastery of Saint John the Theologian on the island of Patmos in Greece.