This book constitutes the refereed proceedings of the Second International Workshop on Principles and Practice of Semantic Web Reasoning, PPSWR 2004, held in St. Malo, France in September 2004. The 11 revised full papers presented were carefully reviewed and selected from 19 submissions. Among the topics addressed are structures in XML documents, querying and updating XML documents, invoking ontologies into the querying process, manipulating and invoking temporal notions, non-monotonic reasoning, and Web services.