This report summarizes the 2018 NSDUH methods and other supporting information relevant to estimates of substance use and mental health issues, and organized into five chapters. Chapter 1 is an introduction to the report. Chapter 2 describes the survey, including information about the sample design; data collection procedures; and key aspects of data processing, such as development of analysis weights. Chapter 3 presents technical details on the statistical methods and measurement, such as suppression criteria for unreliable estimates, statistical testing procedures, and issues for selected substance use and mental health measures. Chapter 4 covers special topics related to prescription psychotherapeutic drugs. Chapter 5 describes other sources of data on substance use and mental health issues, including data sources for populations outside the NSDUH target population. Appendix A is a glossary that covers key definitions for use as a resource with the 2018 NSDUH reports and detailed tables. Appendix B provides a list of contributors to the report.