The economic thought has been developed through the revolutionary or reformist contributions of economists. John Kenneth Galbraith is an economist who has contributed to the development of economic thought in a reformist way. He is a reformer because he approaches the views of economic movements with an inquisitive, critical and modifier perspective instead of believing in them completely and absolutely. He is one of the the pioneers of the reactions against the review of classic economic thought by abstracting it from the institutional structures without economics, time and space. In this respect, contributions of Galbraith to Institutional Economic Thought is incontrovertibly important. The purpose of this study is to examine the contribution of Galbraith to the change of economic thought. The functioning, development, defects and evolution of the economic system are the starting points of the formation of Galbraith's economic thought. In this context, innovations and concepts introduced by Galbraith to the economic thought are explained within the study.