The majority of Muslims call themselves Sunnis, but few know the implications of this affiliation and the dogma of this movement which represents Muslim orthodoxy. However, Sunnism is an important concept which is defined in relation to other deviant currents and also in relation to the dogmatic doctrines that the scholars of orthodoxy have adopted. This present work addresses the conceptual and doctrinal foundations of Sunnism as well as the position of this Orthodox movement in the face of heresies and deviances that have appeared throughout history. This book is therefore essential for any Sunni wishing to better understand their religious affiliation, but also for any non-Sunni Muslim who will learn, through the evidence developed by the author, that authentic Islam is represented by Sunnism.