Artificial Intelligence is the field of computer science that deals with the design of intelligent computational systems, that is, systems that exhibit characteristics we associate with intelligence in human behavior. The book approaches Artificial Intelligence by defining the problems it faces, describing ways of representing knowledge for them, and algorithms for searching their solutions. Additionally, it presents classic applications historically belonging to the area, such as action planning, machine learning, knowledge systems, as well as more modern applications like intelligent agents and the semantic web. The book is complemented with algorithms and examples of Artificial Intelligence applications implemented in PROLOG and CLIPS, two widely used programming languages in the field. The primary purpose of the book was to serve as an educational aid for teaching an introductory course in Artificial Intelligence. The first edition was widely accepted by almost all Computer Science Departments in higher education. In the second edition, the material was restructured to facilitate teaching, and existing topics were upgraded, viewed from a new perspective. Finally, new topics of great research and commercial interest were added, making the book suitable for use in specialized undergraduate or postgraduate courses. The third edition is accompanied by a CD with slides, programs, and algorithm implementations, multimedia educational material, a glossary of terms, etc. The book is supported online at AIBOOK.CSD.AUTH.GR. [Excerpt from the text on the back cover of the edition]