"Anything happens must have its own reason ". Although I cannot really recall exactly when I heard of this statement for the first time, it is always in my mind and in fact it has been one of the motivations for me to carry out research and study. When I asked myself again about the purpose of writing this book at the time of writing this preface, several "add on" rea sons that had never occurred to me at the start of writing this book in the spring of 2003 surprisingly came up. Back then, when I was preparing the progress report for the i JADE (2. 0) project, a "fuzzy" idea of whether it was feasible to write a book on intelli gent agents came to my mind. This book not only would discuss and deal with the theory but also the "spin off" applications from the i JADE pro ject, including: the i JADE Weather Man, the i JADE Stock Advisor, the i JADE Surveillant and the latest works on i JADE Negotiator. The fact that I had to launch the i JADE development kit officially over the Web in the summer of 2003 (http://www. ijadk. org) and to arrange courses and semi nars to teach and train our undergraduate students to make use of this tool kit further supported the idea and the future use of this book. Hence, the "archetype" of this book emerged.