The use of case study methodology as a research strategy in social studies, especially in small scale research, is spreading out rapidly. The aim of case study is to establish a relation between library research and real life.information, in order to release the principles and scientific theories from universities and research centers.A case or theorem is a written narration of some research which existed before and it is not a kind of situation that has come to existence artificially.Furthermore, it has no similarity with experimental research, in which the variables are manipulated in order to measure the influence of a particular element. A case study is a multilateral and profound research accomplished by using qualitative research methods on a social phenomenon.In this article, it is attempted to analyze the different aspects of the method, background, definitions, characteristics types, advantages and disadvantages of case study and its applications as a research strategy.