The articles in this special issue were inspired by the Second East–West Conference on Tobacco and Alcohol Use, which was held April 5–6, 2005 in Pasadena, California. The conference was hosted by the University of Southern California’s Institute for Health Promotion & Disease Prevention Research (IPR), its Pacific Rim Transdisciplinary Tobacco & Alcohol Use Research Center (PR TTURC), and its Transdisciplinary Drug Prevention Research Center (TPRC). With its theme of Culture, Environment, and Genes, the overarching goal was to provide a forum for basic, clinical, and community-based scientists and public health leaders in the United States and Pacific Rim nations to present trends and emerging issues in tobacco and alcohol use in the Pacific Rim; share recent findings in tobacco and alcohol control and prevention research and practice; inform public health applications in prevention and treatment; and facilitate new transdisciplinary collaborations among tobacco and alcohol researchers and public health leaders. Research findings and public health experience have made it abundantly clear that no single level of science can adequately address the puzzle of dependence and addictive behavior, nor can either scientists or public health officials alone address society’s needs regarding tobacco and alcohol prevention and control. The purpose of this conference was to bring together leading scientists and public health workers for collaborative discussions of issues related to tobacco and alcohol that affect the health of people throughout the world. Pacific Rim nations offer a unique laboratory for studying tobacco and alcohol use and dependence. They are home to a large proportion of the world’s tobacco and alcohol users, yet substance use prevention and cessation programs are still in their infancy in many countries. Social norms around substance use in many Pacific Rim cultures are very different from those in many Western cultures, so it is possible to examine the roles of more proximal risk and protective factors, and the effects of interventions across cultural contexts. The population prevalence of genetic variants associated with substance use differs across populations, so it is possible to identify individuals with especially high or low risk for tobacco or alcohol dependence. In addition to fulfilling an important public health need worldwide, research in the Pacific Rim can inform prevention, cessation, and policy efforts in the United States and other Western countries, where large numbers of immigrants from the Pacific Rim settle every year. Although the conference focused on tobacco and alcohol use in Pacific Rim nations, comparisons also were made with North American and European countries. The conference addressed tobacco use from multiple levels—from the molecular to the cultural— and addressed tobacco use etiology, prevention, treatment, and policy at all levels. Speakers and participants came from 10 countries on four continents, including the Pacific Rim areas of East and Southeast Asia, Australia, the Pacific Islands, North America, and Europe. Some of the world’s leading