The purpose of this article is to understand the mission theology of Orlando E. Costas(1942?1987). He was born in Puerto Rico, June 15, 1942 within a sincere Methodist family. When Costas was twelve his family immigrated to the United States and he experienced huge cultural differences, which affected him mostly in negative ways. He had three different conversions in his life. The first took place in 1957 during the Billy Graham`s New York Crusade and the second was the rediscovery of his Hispanic American cultural heritage. The last was his conversion to the World when he was a Latino pastor in Milwau- kee. Costas interpreted Jesus Christ from the ``underside`` of history and the witness of the biblical tradition. Then he examined a meaning of Christ from Galilee. The mission of Christ in Galilee demonstrates His identity, which was identified with the powerless and the oppressed. It implies that starting in the periphery or working from the bottom up can the good news of God`s Kingdom be clearly demonstrated and credibly announced as a message of liberation, justice and peace. The death of Jesus outside the gate implies a new place of salvation. He accomplished the salvation of whole creatures outside the sacred place, which was normally unclean for the Jewish people. The Lord invited His faithful people to go to him outside the camp, bearing the disgrace he bore. For Costas, the mission of God is no personal spiritualistic and non-historical action. Instead, it aims towards and realized in the concrete situation of the World. He argued that the mission of God is not only eschatological but also historical. It transforms human beings not only religiously but also socially, psychologically and culturally as well. When Christ accomplished this mission He did not consider equality with God, although Christ was being in very nature God. And He humbled himself and became obedient to death on a cross. Costas acknowledged the necessity and significance of the growth of Church, but he wanted to clear the reason of it. For him, Church growth is deeply related to the mission of God. And the Church growth is a penultimate goal of its mission but the ultimate is the hope of the final consummation of God`s kingdom. In this sense, Costas stressed that the church itself is a direct result of the missionary action of God`s mission, so all church members should participate in His mission as a faithful missional community.