This methodology transfer paper on case study evaluations describes how GAO evaluators could use case study methods in performing our work. It describes six applications of case study methods, including the purposes and pitfalls of each, and explains similarities and differences among the six. This paper presents an evaluation perspective on case studies, defines them, and determines their appropriateness in terms of the type of evaluation question posed. The original report was authored by Lois-ellin Datta in April 1987. This reissued (1990) version supersedes the earlier edition.