New technologies and approaches, such as data collection with smartphones and censors, are producing data sets that are rich with information that could be used to create a new generation of interventions for drug abuse and HIV prevention and services. However, statistical analysis methods, the keys investigators use to open the door to the scientific knowledge contained in behavioral data, have not kept up with the complexity of modern data sets and the sophistication of the questions posed by today's behavioral researchers. The focus of the proposed Center for Complex Data to Knowledge in Drug Abuse and HIV Behavioral Science (CD2K Center) is development and dissemination of the innovative statistical methods that are essential to unlock the knowledge contained in complex behavioral data and apply it in the fight against drug abuse and HIV. We propose a set of three exciting, thematically integrated research projects, each developing innovative methods for analysis of complex data. We also propose three cores to support and enhance the research, disseminate the innovative methods broadly, and attract and mentor newcomers to the field of behavioral drug abuse and HIV methodology. The overall Specific Aims of the CD2K Center are (A) To develop innovative methods for analysis of complex data that will be tailor-made to inform sophisticated, powerful, and efficient behavioral interventions for drug abuse and HIV prevention; increase knowledge about the etiology of behaviors related to drug abuse and HIV; and guide more effective delivery of drug abuse and HIV intervention services. The methods developed will facilitate the acquisition of highest quality empirical evidence based on complex data. (B) To apply the innovative methods developed in Aim A in existing drug use and HIV data sets, for the purpose of advancing behavioral science in the areas of prevention of drug abuse and HIV, drug abuse and HIV etiology, and delivery of drug abuse and HIV intervention services. We will work with a vibrant network of drug abuse and HIV scientists on empirical studies using the data they have collected and publish the results in peer-reviewed outlets. (C) To serve as a national resource by placing the innovative methods developed in the CD2K Center in the hands of drug abuse and HIV scientists worldwide. (D) To serve as a national resource by nurturing the current and next generations of quantitative methodologists devoted to the study of drug abuse and HIV prevention, epidemiology, and services delivery. In sum, the CD2K Center will quickly become an energetic and fresh national resource for innovative statistical methods for complex data. These cutting- edge methods will enable scientists to address, for the first time, a host of exciting research questions about the behavioral dynamics and factors that underlie drug abuse and HIV, and ultimately pave the way for a new generation of highly effective interventions that will reduce the prevalence and incidence of drug abuse and HIV infection.