This thesis attempts to treat four problems: What is the gospel, as defined in Latter-day Saint literature? Do ancient and modern sources agree? Has there been an historical development of the definitions? Can any disagreements be rationalized? The results of this research reveal that the gospel is complex in that it is capable of handling all the problems of eternity, yet it is simple in that it is a plan of specific principles which lead man step by step to perfection. The author determined that ancient and modern sources do agree in placing six "first principles" at the beginning of man's gospel knowledge, but they then add many advanced principles of the gospel to aid man in his climb to eternal life. In the broad sense of the term, the gospel does include all truth, but all truth in a systematic structure. There has been an historical development of the definitions, for they gradually became more explicit in including all truths and principles. The differences in definitions are apparently due to the progressive revelation of principles, and to the authors' efforts to teach the principles needed by their audiences.