The promise of the Semantic Web is to move from a Web of data to a Web of meaning and distributed services. This vision of the Web has attracted - searchersfromdi?erent horizonswith the aims of de?ning newarchitecturesand languages necessary to make it possible, and of developing the ?rst applications of these concepts. This book contains the articles selected for publication and presentation at the workshop Principles and Practice of Semantic Web Reasoning PPSWR 2005, together with three invited talks. Three major aspects of Semantic Web research are represented in this selection:...