Many Christians consider it their obligation to follow what is often termed the "Great Commission" of Jesus Christ, recorded in the final verses of the Gospel of Matthew: "Go to all the nations and make disciples. Baptize them and teach them my commands." The early Christians were noted for their evangelizing work.
In the Bible, the word proselyte denotes a person who has converted to the Jewish religion, without overtly negative overtones. In our day, however, the connontations of the word proselytism are almost exclusively negative. Nonetheless, many people use the words interchangeably. An Orthodox writer, Stephen Methodius Hayes has written: "If people talk about the need for evangelism, they meet with the response, "The Orthodox church does not proselytize" as if evangelizing and proselytism were the same thing."
The difference between the two terms is not easily defined. What one person considers legitimate evangelizing, or witness bearing, another may consider intrusive and improper.
Illustrating the problems that can arise from such subjective viewpoints is this extract from an article by Dr. C. Davis, published in Cleveland State University's 'Journal of Law and Health': "According to the Union of American Hebrew Congregations, Jews for Jesus and Hebrew Christians constitute two of the most dangerous cults, and its members are appropriate candidates for deprogramming. Anti-cult evangelicals ... protest that 'aggressiveness and proselytizing . . . are basic to authentic Christianity,' and that Jews for Jesus and Campus Crusade for Christ are not to be labeled as cults. Furthermore, certain Hassidic groups who physically attacked a meeting of the Hebrew Christian 'cult' have themselves been labeled a 'cult' and equated with the followers of Reverend Moon, by none other than the President of the Central Conference of American Rabbis". 
Views on the propriety of proselytism, or even evangelism, differ radically. Some feel that freedom of speech should have no limits and that virtually anyone, anywhere should have the right to talk about anything they see fit. Others see all sorts of evangelism as a nuisance and an intrusion and would like to see them proscribed. Thus, Natan Lerner observes that the issue is one of a clash of rights - the right of a person to express his views versus the right of a person not to be exposed to views that he does not wish to hear.
From a legal standpoint, there do appear to be certain criteria in distinguishing legitimate evangelization from illicit proselytism:
Hence a category of improper proselytizing can be discerned.
Since the collapse of the former Soviet Union and the rise of democracy in the Eastern Block, the Russian Orthodox Church has enjoyed a revival. However, it takes exception to what it considers illegitimate proselytizing by the Roman Catholic Church, the Salvation Army, Jehovah's Witnesses and other religious movements  in what it refers to as its canonical territory.
Greece has a long history of conflict, mostly with Jehovah's Witnesses but also with some Pentecostals over its laws on proselytism. This situation stems from a law passed in the 1930s by the dictator Ioannis Metaxas. A Jehovah's Witness, Minos Kokkinakis, won the equivalent of US $14,400 in damages from the Greek state after being arrested repeatedly for the 'offence' of preaching his faith from door to door. In another case, Larissis vs. Greece, a member of the Pentecostal church also won a case in the European Court of Human Rights.
See also: Religious conversion
For a discussion of some of the legal aspects of defining illicit proselytism, see the article Proselytism, Change of Religion, and International Human Rights, by Natan Lerner, PhD