The marriage of epidemiology and prevention has long been recognized and encouraged in public health. This marriage took place in the 18th and 19th centuries with observations such as those of Bernoulli, who determined the long-term effects of smallpox inoculation; Snow, who associated the outbreak of cholera in London with the use of a particular water pump; Louis, whose studies on bloodletting altered medical practice; and Simmelweis, who pointed out the relationship between puerperal fever and the fact that medical staff did not wash their hands with soap or disinfectant between performing autopsies and delivering babies (Lilienfeld & Lilienfeld, 1980). The marriage of epidemiology and prevention of drug abuse had also been proposed but was never fully consummated until the 1970s with the funding of general-population surveys and longitudinal studies that followed youngsters through their high risk-years into early adulthood. Such studies led to the development of causal hypotheses and theories about the etiology of drugabusing behaviors to guide prevention programming and research, but large gaps remain in our knowledge of drug-abuse epidemiology and drug abuse prevention. The goal of this chapter is to establish a link between drug abuse epidemiology and drug abuse prevention and show what contributions epidemiology has made to the field of prevention research and practice. It provides examples from past and current research and offers recommendations for further research. The emphasis is on research, however, and how this research can be translated for, and to, prevention practitioners.