The primary purpose of this book is to bring to the attention of members of the medical and scientific communities, as well as to other interested persons, a new and expanding area of investigation that features the use of chemicals for the prevention of tumor induction and development. This novel use of chemical compounds has succeeded in producing a remarkable series of discoveries in recent years. Some of these are beginning to be evaluated in the field of clinical oncology in a manner that has potentially enormous public health implications. It is anticipated, therefore, that increasing amounts of time, energy, and financial resources will be devoted to the further development and expansion of this work. The major contribution of this book at the present time is that it summarizes and brings up to date the pioneering efforts of the various scientists who originated this new and exciting field of scientific activity. The thoughts expressed by Louis Pasteur in 1884 may soon be applicable in the fight against cancer: "When meditating over a disease, I never think of finding a remedy for it, but instead a means of preventing it. " The emphasis on cancer prevention currently underway is the result, in part, of an increased awareness that the environment-geographical, cultural, and occupational-has a role in development of the disease.