A Christian missionary can be defined as "one who is to witness across cultures". The Lausanne Congress of 1974, defined the term, related to Christian mission as, "to form a viable indigenous church-planting movement". Missionaries can be found in many countries around the world.
In the Bible, Jesus is recorded as instructing the apostles to make disciples of all nations (Matthew 28:19–20, Mark 16:15–18). This verse is referred to by Christian missionaries as the Great Commission and inspires missionary work.
The Christian Church expanded throughout the Roman Empire already in New Testament times and is said by tradition to have reached even further, to Persia (Church of the East) and to India (Saint Thomas Christians). During the Middle Ages the Christian monasteries and missionaries such as Saint Patrick (5th century), and Adalbert of Prague (ca 956-997) propagated learning and religion beyond the European boundaries of the old Roman Empire. In 596, Pope Gregory the Great (in office 590-604) sent the Gregorian Mission (including Augustine of Canterbury) into England. In their turn, Christians from Ireland (the Hiberno-Scottish mission) and from Britain (Saint Boniface (ca 675-754), and the Anglo-Saxon mission, for example) became prominent in converting the inhabitants of central Europe.
During the Age of Discovery, the Catholic Church established a number of missions in the Americas and in other Western colonies through the Augustinians, Franciscans, and Dominicans to spread Christianity in the New World and[clarification needed] to convert the Native Americans and other indigenous people. About the same time, missionaries such as Francis Xavier (1506–1552) as well as other Jesuits, Augustinians, Franciscans, and Dominicans reached Asia and the Far East, and the Portuguese sent missions into Africa. Emblematic in many respects is Matteo Ricci's Jesuit mission to China from 1582, which was totally peaceful and non-violent. These missionary movements should be distinguished from others, such as the Baltic Crusades of the 12th and 13th centuries, which were arguably compromised in their motivation by designs of military conquest.
Much contemporary Catholic missionary work has undergone profound change since the Second Vatican Council of 1962-1965, with an increased push for indigenization and inculturation, along with social justice issues as a constitutive part of preaching the Gospel.
As the Catholic Church normally organizes itself along territorial lines and had the human and material resources, religious orders, some even specializing in it, undertook most missionary work, especially in the ear after the collapse of the Roman Empire in the West. Over time, the Holy See gradually established a normalized Church structure in the mission areas, often starting with special jurisdictions known as apostolic prefectures and apostolic vicariates. At a later stage of development these foundations are raised to regular diocesan status with a local bishops appointed. On a global front, these processes were often accelerated in the later 1960s, in part accompanying political decolonization. In some regions, however, they are still in course.
Just as the Bishop of Rome had jurisdiction also in territories later considered to be in the Eastern sphere, so the missionary efforts of the two 9th-century saints Cyril and Methodius were largely conducted in relation to the West rather than the East, though the field of activity was central Europe.