The National Treatment Center Study (NTCS) is a longitudinal federally funded research project on treatment organizations.The National Treatment Center Study is a family of related projects in the area of addiction health services research. Each study is designed to document and track changes in the organization, structure, staffing, and service delivery patterns of substance abuse treatment programs throughout the U.S. The primary focus in each study is on the organizational factors associated with the use of “evidence based practices,” including psychosocial counseling approaches, pharmacotherapies, and wraparound services. Each project has its own unique area of emphasis; some focus on specific types of treatment programs (e.g., programs in the Clinical Trials Network, opioid treatment programs, therapeutic communities) while others focus on the delivery of specific types of treatment services (e.g., smoking cessation services, adolescent programs). This research is one of the most enduring and referenced bodies of work in the field and translates directly to policy at a national level.