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 New Testament-era missionary outreach of the Christian church from the time of St Paul expanded throughout the Roman Empire and beyond 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 Roman Catholic Church established a number of missions in the Americas and in other colonies through the Augustinians, Franciscans, and Dominicans to spread Christianity in the New World and 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 started moving into Asia and the Far East. The Portuguese sent missions into Africa. These are some of the most well-known missions in history. While some missions accompanied imperialism and oppression (the Baltic Crusades of the 12th and 13th centuries, for example), others (notably Matteo Ricci's Jesuit mission to China from 1582) were relatively peaceful and focused on integration rather than on cultural imperialism.
Much contemporary Catholic missionary work has undergone profound change since the Second Vatican Council of 1962-1965, and has become explicitly conscious of social justice issues and the dangers of cultural imperialism or economic exploitation disguised as religious conversion. Contemporary Christian missionaries argue that working for justice forms a constitutive part of preaching the Gospel, and observe the principles of inculturation in their missionary work.