After being introduced as an academic concept by political sociologist Nathan Leites in 1951 during the Cold War, many scholars have tried to define “operational code” in various ways, primarily to solve puzzles about why decision-makers engage in blunders. A review is provided of how the term has been used, albeit differently, by such scholars as J. David Singer, Ole Holsti, Alexander George, W. Michael Riesman, John Lewis Gaddis, Lucian Pye, Stephen Walker, and many others. Despite attempts to standardize operational code research, including psychological and sociological formulations as well as role theory, their theoretical approaches have failed to converge on a common theme, needing a solution.