The oral cavity includes the vermilion borders of the lips, labial mucosa, buccal mucosa, buccal vestibule, alveolar ridges and gingiva, floor of mouth, oral tongue, and hard palate. The problem of oral cancer is increasing in some countries and usually associated with diverse risk factors. The challenge of oral cancer is that, it is often diagnosed late at an advanced stage, when it becomes difficult to treat causing high morbidity rates. Because oral cancer can spread quickly, early detection is important. Examining an oral cancer can identify early signs of this disease. Pathogenesis of oral cancer is attributed to the cumulative effect of many molecular and biochemical cellular abnormalities, as well as immune system alterations and changes in the underlying connective tissue. Precancerous conditions are associated with a greater-than-normal risk of development of a potentially malignant lesion or cancer in affected tissue. Advances in research on potentially malignant lesions of the oral cavity are leading to earlier diagnosis, appropriate treatment, and enhanced follow-up.