This book constitutes the refereed proceedings of the First International Conference on Rules and Rule Markup Languages for the Semantic Web, RuleML 2005, held in Galway, Ireland in November 2005 co-located with the 4th International Semantic Web Conference, ISWC 2005. The 18 revised full papers presented together with 2 invited talks were carefully reviewed and selected from around 30 submitted papers. The papers present information about requirements, applications, technology solutions, and the latest research on rule languages and standards, with the ultimate goal of advancing a standard framework for Semantic Web rules - critical to the early adoption and applications of knowledge-based techniques in e-business, especially enterprise integration and B2B e-commerce. This includes knowledge representation (KR) theory and algorithms; markup languages based on such KR; engines, translators, and other tools; relationships to standardization efforts; and, not least, applications.