Monasticism in Christianity is a family of similar traditions that began to develop early in the history of the Christian Church, modeled upon scriptural examples and ideals, but not mandated as an institution by the Scriptures.

While most people think of Christian or Catholic monks or nuns as "something to do with living in a monastery", from the Church's point of view the focus has nothing to do with living in a monastery or performing any specific activity, rather the focus is on an ideal called the religious life, also called the state of perfection. This idea is expressed everywhere that the things of God are sought above all other things, as seen for example in the Philokalia, a book of monastic writings. In other words, a monk or nun is a person who has vowed to follow not only the commandments of the Church, but also the evangelical counsels (e.g., vows of poverty, chastity, and obedience). The words of Jesus which are the cornerstone for this ideal are "be ye perfect like your heavenly Father is perfect".

The first efforts to create a proto-monastery were by Saint Marcarius, who established individual cells, an example Kellia founded in 328, known as "larvae", the purpose of which was to bring together individual ascetics who, although pious, did not have the physical ability or skills to live a solitary existences in the desert like that of Saint Anthony. These cells were put together as a large single monastic community by Saint Pachomius around 323 in upper Egypt at Tabennesi. Guidelines for daily life were created, and separate monasteries created for men and women. He was hailed as Abba ("father", from which we get the word Abbot). This one community was so successful he was called in to help organize others and by one count by the time he died in 346 there were thought to be 3000 such communities dotting Egypt, especially the Thebaid. Within the span of the next generation this number increased to 7000. From there it quickly spread out first to Palestine and the Judean Desert, Syria, North Africa and eventually the rest of the Roman Empire where it became a central aspect of life during the Middle Ages. The first non-Roman area to adopt the system was Ireland, which developed a unique form closely linked to traditional clan relations, a system that later spread to other parts of Europe, especially France.

The ascetic monasteries required rules to live by and in the eastern half of the Roman Empire the rules were created by Saint Basil of Caesarea, called the ascetic rule, or Ascetica. It is the rule still used today in the Orthodox Church. In the West the rules were set a few generations later by Saint Benedict of Nursia who created the Rule of Saint Benedict at his monastery in Monte Cassino, it would become the most common rule throughout the Middle Ages, spawning many other Orders, and it is still in use today.

Monasteries were initially seen by the Church Bishops and imperial governments in Constantinople and Rome as operating outside the authority of the official Church governance, not to mention the Emperor. There existed a tension between the lay clergy and the monastic orders. Eventually over the course of the Early Middle Ages the monastic clergy came to infiltrate the regular Church. Thus the golden age of Christian monasticism lasted from about the eighth to the twelfth century. During this century the monasteries developed an almost complete monopoly on prayer and religion in general. The monasteries became an essential part of society as the main intermediary between people and God. This activity brought considerable wealth and power. The monasteries also attracted many of the best people in society and during this period the monasteries were the central storehouses and producers of knowledge.

The system broke down in the eleventh and twelfth centuries as religion began to change. Religion became far less a preserve of the religious elite. This was closely linked to the rise of mendicant orders such as the Franciscan friars, who were dedicated to spreading the word in public, not in closed monasteries. Religious behavior changed as common people began to take communion and actively participate in religion. The growing pressure of the nation states and monarchies also threatened the wealth and power of the orders.

Monasticism continued to play a role in Catholicism, but after the Protestant reformation many monasteries in Northern Europe were shut down and their assets seized. (see Dissolution of the Monasteries).

The legacy of monasteries outside remains an important current in modern society. Max Weber compared the closeted and puritan societies of the English Dissenters, who sparked much of the industrial revolution, to monastic orders.
Many Utopian thinkers (starting with Thomas More himself) felt inspired by the common life of monks to apply it to the whole society (an example is the falansterium).

Modern universities have also attempted to ape Christian monasticism. Even in the new world universities are built in the gothic style of twelfth century monasteries. Communal meals, dormitory residences, elaborate rituals and dress all borrow heavily from the monastic tradition.

Today monasticism remains an important part of the Catholic, Eastern Orthodox and Anglican faith. Vatican II saw major changes to Catholic monasticism including allowing nuns and monks to shed their habits.