Book excerpt: This book constitutes the thoroughly refereed post-proceedings of the 4th International Workshop of the Initiative for the Evaluation of XML Retrieval, INEX 2005, held at Dagstuhl Castle, Germany, in November 2005. The book presents 41 revised full papers, organized in topical sections on methodology, multiple retrieval, ad-hoc retrieval, relevance feedback, natural language queries, and more heterogeneous retrieval, interactive retrieval, document mining, and multimedia retrieval.