These days, Expert systems play vital roles. They are applied components of Artificial Intelligence (AI), aiming to develop computer programs that simulate the thought process of a human expert to solve complex decision problems in a specific domain. Such kinds of systems are applied where knowledge is critical to solve a problem. It involves both factual and heuristic knowledge to solve a problem where a human expert faces difficulty, scarce or unavailable in their operations. The actual development of such systems begins with formulating and representing the knowledge base. Expert system tools are used in the process of building Expert systems. PROLOG is one of the programming languages that can be used in the development of Expert systems. The book introduces the basic concepts of Expert systems and the practical aspects of development in a simple way and is designed to give you quick help on how to build Expert systems from scratch. It presents the various features used in Expert systems, shows how to implement them in Prolog, and how to use them to solve problems.