XML Retrieval Documents usually have a content and a structure. The content refers to the text of the document whereas the structure refers to how a document is logically organized. An increasingly common way to encode the structure is through the use of a mark up language. Nowadays the most widely used mark up language for representing structure is the eXtensible Mark up Language (XML). XML can be used to provide a focused access to documents i.e. returning XML elements such as sections and paragraphs instead of whole documents in response to a query. Such focused strategies are of particular benefit for information repositories containing long documents or documents covering a wide variety of topics where users are directed to the most relevant content within a document.The increased adoption of XML to represent a document structure requires the development of tools to effectively access documents marked up in XML. This book provides a detailed description of query languages indexing strategies ranking algorithms presentation scenarios developed to access XML documents. Major advances in XML retrieval were seen from 2002 as a result of INEX the Initiative for Evaluation of XML Retrieval. INEX also described in this book provided test sets for evaluating XML retrieval effectiveness. Many of the developments and results described in this book were investigated within INEX Introduction Basic XML concepts Element Well formed XML document Document type declaration XML schema XML documents as trees Historical perspectives Structured document retrieval Passage retrieval Structured text retrieval Hypertext and web retrieval Data vs document centric XML documents Querying semi structured data Content oriented XML retrieval INitiative for the evaluation of XML retrieval (INEX) Focused retrieval Query languages Structural constraints Classification of XML query languages Content only Content and structure Examples of XML query languages XPath NEXI XQuery XQuery full text Discussion Indexing strategies Element based indexing Leaf only indexing Aggregation based indexing Selective indexing Distributed indexing Structure indexing Discussion Ranking strategies Element scoring Contextualization Propagation Aggregation Merging Processing structural constraints Discussion Presentation strategies Dealing with overlaps Presenting elements in context Entry points Discussion Evaluating XML retrieval effectiveness Document collections Topics Relevance assessments Retrieval tasks Measures Discussion Conclusions XML element retrieval Beyond XML element retrieval Beyond XML retrieval Bibliography Biography