There are a number of reasons why this book is important. First, there is no one source that summarizes what we know about the prevention of substance abuse from the research field, so the book serves as a repository of accumulated knowledge on prevention theory, intervention design, and development and prevention research methodology. Second, as an evolving field, prevention science has only begun to assert itself in both the arenas of practice and policy. The formation of the Society for Prevention Research in 1991 was the first recognition that a science of prevention existed and required a separate forum to present the rapidly growing content of the field for dis­ cussion and review. Finally, there is a need to establish a baseline, a reference point against which progress in the field of prevention science can be assessed. This book serves all of these purposes. The idea for this book grew from the observation in the early 1990s that after decades of attempts to develop effectiveinterventions to prevent drug use among children and adolescents in the United States that we were finally having success, particularly in addressing the initiation of use. These successes are the result of research that has provided a better understanding of the factors and processes associated with the onset of substance use.