This study aims at defining the concept of OPAC, tracing of research trends and development of it, and clarifying various methods of subject access and patterns of bibliographic searching in OPAC as well as strategies for improving to implement online catalogs. Although OPAC is so far the most user-friendly bibliographic searching method, there are still a lot of issues including online subject access in particular. Therefore a more effective and useful method for computer end-users have to be developed, for instance, improvement of an indexing system, a n.0, pplication of the classification system as a searching tool, a new design and construction of standardized thesaurus, betterment of user interface, introducing of expert system into bibliographic searching, establishment of subject authority file. Those would raise the success-rate of users seeking bibliographic information in the library catalogs. Korean libraries are in very early stage of OPAC implementation so that every efforts and concerns to improve strategies and techniques for subject access to OPAC have been strongly asked.