At GESIS we conduct basic and applied research in the field of survey methodology. Our survey research is divided into the focus areas of Survey Statistics, Survey Instruments, Survey Operations and Comparative Surveys. We pursue the goal of gaining evidence-based insights into how surveys and their data quality can be optimised. Within the framework of systematic reviews and meta-analyses, we evaluate existing research and identify research gaps. In the research area of survey methodology, we also explore the connection of survey data with digital behavioural data (e.g. social media profiles, smartphone usage data or browsing histories) and examine how these data types can be complemented and combined. To this end, we are also driving the transfer of established concepts for assessing the data quality of surveys to digital behavioural data.