Case study research is an increasingly used research strategy in several academic disciplines, undertaken with the purpose of researching the phenomenon within a real-life context. A case study aims to analyse a spatially and temporally bounded case, to enable an in-depth understanding. Despite the growth of methodological literature, the concept of case study has been criticised for being fuzzy, and questions about the credibility of case study research have been raised. This chapter addresses issues of ontology, epistemology, and methodology that are central to the principles of case study design, with references to ongoing debates in the literature.