The combined effect of chewing tobacco (areca quid chewing) alcohol drinking and smoking greatly increase the risk of Oral Precancerous Disorders (like Leukoplakia, Erythroplakia, Oral submucous fibrosis and Verrucous lesions) in oral cavity. In developing countries of South East Asia, Indian people develop more oral precancerous disorders like Leukoplakia, Erythroplakia, Oral submucous fibrosis and Verrucous lesions compare to many other developed countries. It is estimated that in India 75% of cancers of oral cavity are attributable to tobacco chewing, smoking and alcohol drinking. So the purpose of this book is to present the correlations of these premalignant disorders microscopically with in tobacco users and alcohol drinkers.