This book is an extensive, evidence-based, in-depth review of all aspects of the frequent oral potentially malignant disorder Oral Lichen Planus, from the complex pathogenesis and differential diagnosis to therapeutic management. It highlights the main discoveries and the limits of current knowledge in the epidemiology, pathogenesis and therapy of this oral disorder, projecting clinicians to the best possible therapeutic management and researchers to the main research fields potentially interesting for the understanding of etiopathogenesis and the establishment of a universally recognized diagnostic criteria. Detailed orientation is provided on oral lichen planus and on the main oral disorders clinically and histologically very similar to it. This work is aimed at clinicians, who are often faced with oral lesions that are not always easily diagnosed, and researchers who are interested in dentistry, oral medicine, and the partly mysterious disease Oral Lichen Planus.