Teaching a large number of ever-inspiring students for the past few years was the motivation for the author to compile this book. This book would not have seen the light of the day if it were not for them. Knowledge of the pathogenesis of the various diseases affecting the oral cavity offers a great help in understanding its clinical features, its radiographic features, and histological features as well as the treatment for the diseases. These are the reasons for the necessity to compile various pathophysiological causes of the diseases. Some of the diseases are still being explained by their old pathogeneses; however, some others are being attributed to new causes following the advent of new and innovative technologies, which identify genes and new knowledge about stem cell culturing. This book simplifies the subject of Oral Pathology by understanding the underlying causes of the various diseases.