The purpose of this thesis is to examine why social scientists choose to reuse research data. Through semi-structured interviews with researchers with previous experience of data reuse, this thesis seeks to illuminate the factors that influence their decisions. The interviews were analysed using qualitative content analysis. The theoretical framework consists of concepts borrowed from two theories. The first is a model for data sharing, that has been applied to data reuse. The second is a theory of satisfaction with data reuse. The results show that the most influential factors are ethical and financial aspects, and the accessibility of the data itself. Together with the literature review, the results suggest that the way forward is to develop a functioning infrastructure for data sharing, to facilitate the discovery of data for reuse.