Most of us would agree that intrinsic motivation is one of the most important concepts in educational practice. Unfortunately, however, as some researchers have suggested, the concept of intrinsic motivation is so ambiguous that it is very difficult to distinguish it from similar motivational concepts such as the Origin-Pawn and Locus of Control conceptualizations. The purpose of this paper is to make the concept clear by considering trends in conceptualizations of and studies on intrinsic motivation from historical point of view. It is found that the main issue of the studies shifted from “cognitive motivation”(what makes tasks interesting) to “undermining and enhancing effects” of interpersonal and evaluative variables. It is concluded that intrinsic motivation is defined as a motivational state in which learning is undertaken for its own sake and that the mastery orientation and autonomy are its essential components.