The integrity of the oral mucous membrane is maintained by a wide range of complex factors including those dependent on adequate nutrition. Oral cavity is considered the mirror of the body. Pigmentation of oral mucous membrane range from the extremely common and harmless lesions to the rare and deadly lesions. They may be physiologic or an indicator of local disease or a sign of systemic disease. It is caused by various Endogenous or Exogenous factors. They are usually asymptomatic and diagnosing the lesion early remains the key to proper management. To arrive at definite diagnosis, complete history, biopsy and laboratory investigation if required should be utilized. The recognition, identification and clinical assessment of pigmentation is of great importance. This book reviews extensively the various pigmented lesions of the oral mucosa.