Efforts to develop knowledge-based systems have now been pursued for over two decades. Languages, inference methods, architectures, and tools have reached a certain standard and have led to interesting and successful applications. Nevertheless, there is still some mystery and confusion among the public about this area. The purpose of this article is to provide a short and simple but nonetheless informative description of the topic including some indications of present trends in research. It should also be remarked that knowledge-based systems (as well as other techniques coming from artificial intelligence) are in no way mysterious and could be understood without knowing what “intelligence” really is. They are nothing more than problem solving methods which have some interesting and (sometimes) new features.