The Qurʾān and the Sunnah of the infallible Imams (as) have consistently been recognized as the primary sources for understanding Islam. Nevertheless, throughout Islamic history, certain perspectives have emerged asserting that the Qurʾān alone suffices for comprehending the religion, rendering the Sunnah and prophetic traditions unnecessary. This approach, commonly known as “Qurʾān-only” or Qurʾān sufficiency, poses significant challenges and produces far-reaching consequences across exegetical, social, cultural, and juridical domains. Employing a descriptive-analytical methodology, this article investigates the concept of Qurʾānism, its historical and doctrinal scope, and its adverse implications. Among these consequences are misinterpretation and partial understanding of the Qurʾān, the rise of extremist exegesis, the weakening of the spirit of ijtihād and jurisprudential creativity, and the deepening of intra-Muslim divisions. Furthermore, the neglect of Sunnah and Ḥadīth traditions may lead to violations in the realization of social rights and human justice, intensify juristic disagreements, and generate practical challenges in Islamic law and governance. The study concludes by emphasizing the indispensable necessity of a dynamic interplay between the Qurʾān and Sunnah for a comprehensive and accurate understanding of Islam.