Whether case study research is a legitimate form of research, or merely a focus of research, remains controversial. However, despite the controversies, case study research is still widely used by researchers in various disciplines and academic fields. This suggests that there are strengths of this approach which cannot be ignored. The major concern of this paper is the qualitative single case study. The controversial aspects, including sampling, data collection, analysis, generalization, reliability and validity, of this type of case study are addressed.