Recently surpassing heart disease, cancer is now the leading cause of death (one in four) in the United States. Worldwide, cancer control is becoming increasingly important as life expectancy improves because of lower infant mortality and fewer deaths from infectious diseases. Morbidity and mortality from many forms of cancer can be controlled through primary or secondary prevention. Primary prevention can be defined as risk modification to lower cancer occurrence. Secondary prevention refers to the use of screening tests to detect cancers at early stages. Environmental carcinogens, inherited factors that predispose to cancer, and screening and early detection are covered in major sections. Also included are discussions of infectious agents, occupational carcinogens, iatrogenic causes, carcinogens affecting the reproductive system, and miscellaneous environmental causes. Tables outline established causes of human cancer, common hereditary cancers and syndromes attributable to germline mutations in predisposing genes, and the American Cancer Society’s recommendations for early detection of cancer. This chapter contains 138 references.