Organized effort to spread the Christian faith. St. Paul evangelized much of Asia Minor and Greece, and the new religion spread rapidly along the trade routes of the Roman Empire. The advance of Christianity slowed with the disintegration of the Roman Empire after AD 500 and the growth of Arab power in the 7th–8th century, but Irish and Anglo-Saxon missionaries continued to spread the faith in western and northern Europe, while missionaries of the Greek church in Constantinople worked in eastern Europe and Russia. Missions to Islamic areas and Asia began in the medieval period, and when Spain, Portugal, and France established overseas empires in the 16th century, the Roman Catholic church sent missionaries to the Americas and the Philippines. A renewed wave of Roman Catholic missionary work in the 19th century focused on Africa and Asia. Protestant churches were slower to undertake foreign missions, but in the 19th and early 20th century there was a great upsurge in Protestant missionary activity. Missionary work continues today, though it is often discouraged by the governments of former European colonies that have won independence.
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The communication of Christian faith to new geographical areas and cultures is often referred to as evangelisation, or specifically, world evangelisation.
Our modern word "Gospel" comes from the old English word, "Godspell." In old English "spell" meant "word" (we carry this meaning also in our word "spelling"). So in other words "Godspell" meant, "God word" or "Word of God." Therefore the Gospel is the good news found in the Word of God.

On the other hand, converting Christians (e.g., Orthodox) who are not churchgoers to another Christian denomination is commonly seen as evangelism, not proselytism.
Catholic missionary work in Russia is commonly seen as evangelism, not proselytism. Archbishop Kondrusiewicz openly stated
"that proselytism is absolutely unacceptable and cannot constitute a strategy for the development of our structures either in Russia or in any other country in the world." 
Especially regarding claims by Orthodox church that spreading the faith and receiving converts amounts to proselytism
Catholic church CDF issued document called " Doctrinal Note on some aspects of evangelisation" which states that evangelism is "an inalienable right and duty, an expression of religious liberty ...", document added that "The incorporation of new members into the Church is not the expansion of a power group, but rather entrance into the network of friendship with Christ which connects heaven and earth, different continents and age. It is entrance into the gift of communion with Christ ..."
Other translations render the phrase “make disciples of all nations” in the above quotation as “teach all nations.” Jesus is also quoted in the Gospel of Mark saying
These are two main passages of the New Testament from God that commands everyone who believes in Christ Jesus to preach the Gospel.
The title of evangelist is often associated with those who lead large meetings like those of Billy Graham, possibly in tents or existing church buildings, or those who address the public in street corner preaching, which targets listeners who happen to pass nearby on the street. It can also be done in small groups or even on a one-to-one basis, but actually it is simply one who spreads the gospel. Increasingly, the Web enables anyone to become an Internet evangelist.
The term is also used in a non-religious sense to describe an individual who takes up a cause and convinces others to it (see technology evangelist). Guy Kawasaki, an author and venture capitalist, describes evangelists as individuals who promote a particular product. At Apple Computer, he was part of a team of Apple evangelists that convinced programmers to develop software on the Macintosh Platform. In The Human Fabric (Aviri, 2004), Bijoy Goswami describes the "Evangelist" as one of three core energies in people and society.