Simplified one could say that expert systems are computer programs that contain certain specific knowledge in one or more specific areas of science. Such programs are commercial and developed by scientist in the field of artificial intelligence. The most common form of the expert system consists of a set of rules by which analyze the information about a specific type of problem, but also of providing a mathematical analysis of the problem. Depending on their performance, provide user specific feedback one need to take in order to address the given problem. Expert systems mostly help in organizations that have a high level of experience and knowledge in direct and proper problem solving that is difficult to convey to the other members of the same organization, or on a third. Such systems are designed to make it easier for you to "convey intelligence", knowledge and information that is held by experts, according to other members of the organization for the purpose of solving the problems. They can find an approximate solution to the problem, even when the information about the problem is incomplete and can explain the way in which they came to the proposed solutions. An important feature of expert systems is their ability to explain the process by which they came up with a solution to the problem. In this way the knowledge they possess and the mechanism of the reasoning they use are becoming understandable to the user, so users can check the process of reasoning used by the expert system.