There are many differences in opinion about determining the origin of contemporary Iranian history. Throughout the Pahlavi period, efforts were made to identify the coup of 1921 and the rise of Reza Shah as the origin of contemporary Iranian history. By drawing a dark picture of the general situation in Iran during the Qajar period, especially the critical situation of the country on the Eve of the coup of 1921, the Pahlavi supporters tried to introduce Reza Shah as the founder of modern Iran and the coup of 1921 as the origin of contemporary Iranian history. The main problem of this article is whether the coup of 1921 and the rise of Reza Shah is the origin of contemporary Iranian history? Evaluating and criticizing the ideas presented about Reza Shah by official historians of the Pahlavi period as well as some independent historians, the author argues that the origin of contemporary Iranian history is not the coup of 1921 or the reign of Reza Shah. Because the modernizations of Reza Shah's period, despite their vast and diversity, contained contradictions that makes Iranian society to internal tensions and crises, and the type of Reza Shah's monarchy belonged to the pre-constitutional period in terms of the logic of historical change and could never include Iran enter to a new era of civilization. Therefore, the origin of contemporary Iranian history is not the coup of 1921, but the Constitutional Revolution.