Oral lichen planus (OLP) is a relatively common mucosal disease that can present isolated or associated with cutaneous lichen planus. Contrarily to its cutaneous counterpart, though, OLP tends to be chronic, relapsing, and difficult to treat. Severe morbidity is related to erosive forms, and more aggressive presentations have been described, such as the "gingivo-vulvar syndrome". This article reviews the current knowledge about the pathogenesis, clinical picture, differential and laboratorial diagnosis, prognosis, and treatment of OLP.