Case studies are a widely used research strategy employed in qualitative research. Having been applied for a long time in social sciences and considering the considerable number of scientific papers dealing with their epistemology, case studies are often discussed in terms of their status, (un)clear definition and application in the context of methods of social science research. The aim of this paper is to contribute to an understanding of this research strategy and to offer to the reader, the future researcher who wishes to conduct a case study, an overview of relevant authors and their views of processes typical for this strategy, which differs from other strategies mostly by the flexibility of its design. In addition to discussing challenges related to the definition for case study, the paper also deals with various principles for selecting cases, methods for collecting data about the case and determining case limits. The paper lists potential methods for ensuring the validity and reliability of case studies and offers advice on reporting about a conducted case study. Finally, the characteristics of case studies are described considering the criterion of flexibility while emphasising the role of the researcher conducting the study.