The use of surveys to assess the type and extent of substance use in various populations is a crucial tool in alcohol and drug research. The Centre for Alcohol and Drug Research has surveyed a variety of populations (national, regional, treatment populations, population sub-groups), used a variety of sampling methods (probability, convenience) and applied various administrative modes (telephone, postal, web, personal interview) to ask people about their use of alcohol and/or of various drugs. A unique advantage of conducting survey research in Denmark is the possibility to link data from surveys with the many data registers that exist in the country, allowing researchers to gain more extensive information on respondents. Current Centre treatment research is linking treatment registries with survey data to better determine treatment needs and deficits. Furthermore, recent Centre surveys are being complemented with depth and focus group interviews. This enables the Centre to gather qualitative data on the same survey respondent and thus create a more detailed picture. Using a variety of data sources to enhance survey data serves to address the limitations and potential biases of survey research data, especially those pertaining to validity and causality. The combination of a variety of perspectives on the same unit of observation aids in strengthening research results.