Book excerpt: Tumors can be induced by a variety of physical and chemical carcinogens. The resulting tumor cells are usually abnormal in their morphology and behavior and transmit their abnormalities to their daughter tumor cells. Most theories of the pathogenesis of tumors suggest that carcinogens in some way cause alterations either of the genomes or of inheritable patterns of gene expression in normal cells, which then cause morphological and behavioral changes. This volume presents a collection of articles aimed at the question by what genetic or epigenetic mechanisms carcinogens can cause morphological abnormalities of tumor cells. It includes reviews of cellular targets of known carcinogens, and presents varying viewpoints of how morphological abnormalities and the actions of carcinogens might be related. The volume will be of interest to all those who are involved in cancer research or in the prevention, diagnosis or management of tumors in humans or animals.