This study has two aims. one is to devide the ideology of reference service into three groups such as conservative, moderative, and progressive theories, and then investigate the validity of each theory as well as any problems to be suggested. The other is to establish appropriate standards of reference service according to the types of libraries and users, based on the analysis of such theories. Each theory has its own merits and demerits. Accordingly, it seems to be difficult to apply uniformly and theory into users who have different types of question and educational levels. And also it is difficult to apply into various libraries which have different aims of establishment, characteristics, and the users of each library. Consequently, it is suggested to set up a norm of reference service according to the types of libraries and users respectively. The conservative theory is applicable to small and medium sized public libraries, school libraries, and college and university libraries of which the users are mainly students and citizens. The progressive theory is desirable for special and academic libraries as well as large public libraries where the users are mainly specialists. and scholars.