Lichen planus is an inflammatory disorder that affects the skin and mucosa. The oral mucous membrane is frequently affected. Even though it is well defined lesion, many reports show subjective variability in diagnosing it. The term lichenoid reaction is the histologic description used to capsulize the pathologic characteristics of skin diseases resembling Oral Lichen Planus. The book touches all the aspects related to Oral Lichen Planus for better understanding of the lesion.