The National Drug and Alcohol Survey (NDAS) collects information on alcohol and tobacco consumption and drug use among the general population in Ireland. It also surveys people’s attitudes and perceptions relating to tobacco, alcohol, and other drug use and records the impact of drug use on people’s communities. The 2019–20 NDAS collected information from 5,762 people aged 15 years and older across Ireland. The rationale for the 2019–20 NDAS was to generate data that estimate the prevalence of drug use and describe patterns of use, as set out in action 5.1.45 of the national drugs strategy. The objective of the 2019–20 NDAS was to determine the prevalence and patterns of drug use (including alcohol and tobacco use) of a representative sample of the general population aged 15 years and older in Ireland, and to compare the current situation with previous surveys. The data collected provide a detailed description of drinking patterns (including hazardous drinking patterns) in Ireland, and the harms associated with alcohol use and estimations of the prevalence of alcohol use disorder as well as data on the perceptions and attitudes of people in Ireland towards alcohol use. Previous drug prevalence surveys were undertaken in 2002–03, 2006–07, 2010–11, and 2014–15. These surveys were commissioned on an all-island basis by the National Advisory Committee on Drugs and Alcohol (NACDA) in the Republic of Ireland, and the Department of Health, Social Services and Public Safety in Northern Ireland. For the first time, the current survey was managed by the HRB and only included the Republic of Ireland.