Lichen Planus is an "eruption of flat topped, shiny, violaceous papules on flexor surface, male genitalia and buccal mucosa of unknown cause, may formed linear groups, microscopically characterised by a band like sub epidermal lymphocytic infiltrate."Oral Lichen Planus is a premalignant condition.They are usually bilaterally symmetrical.Oral lichen planus may coexist with lesions of the genital mucous membranes or with lesions of cutaneous lichen planus.This book aims at reviewing the pathogenesis, etiology, clinical features, histopathology and treatment of oral lichen planus.