This book contains a collection of thoroughly revised tutorial papers based on lectures given by leading researchers at the 4th International Summer School on the Reasoning Web, held in Venice, Italy, in September 2008. The objective of the book is to provide a coherent introduction to semantic web methods and research issues with a particular focus on reasoning. The seven tutorial papers presented provide competent coverage of methods and major application areas such as social networks, semantic multimedia indexing and retrieval, bioinformatics, and semantic web services. They highlight which techniques are already being successfully applied for purposes such as improving the performance of information retrieval algorithms, enabling the interoperation of heterogeneous agents, modelling users profiles and social relations, and standardizing and improving the accuracy of very large and dynamic scientific databases.