個案研究的研究合理性長期以來飽受爭議，不同領域的研究方法學家對於應將之歸類於一種研究形式或研究焦點而有不同見解，而諸多爭議之根本源自於個案研究的取樣、資料蒐集方法、資料分析方法有效性、可靠性及普及性。本文將個案研究飽受爭議之上述各點提出討論，文中以外語教學研究中的質性個案研究方法為討論之要點及背景。

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.