Book excerpt: This book presents the state of the art of research and development of computational reflection in the context of software engineering. Reflection has attracted considerable attention recently in software engineering, particularly from object-oriented researchers and professionals. The properties of transparency, separation of concerns, and extensibility supported by reflection have largely been accepted as useful in software development and design; reflective features have been included in successful software development technologies such as the Java language. The book offers revised versions of papers presented first at a workshop held during OOPSLA'99 together with especially solicited contributions. The papers are organized in topical sections on reflective and software engineering foundations, reflective software adaptability and evolution, reflective middleware, engineering Java-based reflective languages, and dynamic reconfiguration through reflection.