The vermilion of the lips was conceptualized by Jean Darier as the semi-mucosa. The anatomy of the lips is transitional from skin to mucous membrane. This article emphasizes inflammatory diseases of the lips known as cheilitis. Angular cheilitis is a reactive process with several possible causes, including infections, mechanical, nutritional deficiency, and various dermatoses. Contact cheilitis may be caused by a primary irritant or a delayed hypersensitivity allergic reaction to contactants. Plasma cell cheilitis is a reactive periorificial mucositis. Exfoliative cheilitis is also a reactive process, probably secondary to factitious activity of the patient. Cheilitis glandularis is a chronic inflammatory disorder of the labial salivary glands and their ducts. There are three forms: simple, superficial suppurative, and deep suppurative. A premalignant potential is present in cheilitis glandularis. Cheilitis granulomatosa is one manifestation of orofacial granulomatosis. The granulomatous conditions of Melkersson-Rosenthal syndrome, sarcoidosis, and Crohn's disease may be associated with cheilitis granulomatosa or it may stand alone as Miescher's cheilitis. Actinic cheilitis is another premalignant form of cheilitis that is amenable to a variety of therapeutic modalities.