This paper introduce the basic concept of expert system. Even before the world was aware of the importance of the computers, work by Alan Turing in the 1930s, and by John Von Neumannn the 1950sgave rise to captivating notion of Artificial intelligence. Clearly expert systems are more mature and widely used commercial application coming out of artificial intelligence.in an expert system, the computer applies heuristics and rules in a knowledge specific domain to render advice or make recommendations, much like a human expert would. Expert systems are knowledge intensive programs that solve problem in a domain that require considerable amount of technical expert. This paper focus on expert systems, architecture of an expert system, advantages of an expert system.