This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book provides a list of mutagens in food and their detailed accounts. It also contains considerations on the consequences of the presence of such mutagens, particularly the possible carcinogenic hazard to humans. Epidemiological studies show that the major causes of human cancer are diet and tobacco. The presence of mutagens in food and its consequences are clearly important issues for scientists. A goal in the study of food mutagens is to find preventive measures against human exposure to the mutagens. Tap water and well water have been generally regarded as safe. However, the studies have indicated that chlorination of surface water can sometimes produce mutagens. The water of the Yodo has been found to be continuously contaminated with strong mutagens that originate from a sewage plant of the City of Kyoto.