[en] An agent study is variously applied from the restricted research of an early AI field to the practical SW development of the design and implementation of a high level, distributed hybrid system. Among the detailed research fields of AI, making a new research field called distributed AI, the trial of resolving a problem based on an agent, has begun. Related to it, the requirement of an intelligent system to offer convenience to easily do a job which the user wants, with the recent trial of an approach for internet agents of various types, were developed to be performed automatically and the agent anticipate the user's need. In this paper, the basic concepts regarding an agent system, research direction and applications were analyzed and outlined. The consisting elements were also analyzed. such as background, needs, basic concepts and properties of the agent. The agent's research status was recently analyzed, and the development and related property of an intelligent agent were written. Application and the instance of a generalized agent about applicable fields in the real world were studied, functions and services about intelligent agents were analyzed. The applicable field of an agent technique becomes various not in information retrieval on a web site, but in the processing of internet information, and in the electronic commerce, industry and medical fields. Through analyzing and comparing the general concept of various agents, this study will aid in establishing a future direction of research in this field