This chapter introduces the process to retrieve units (or subdocuments) of relevant information from XML documents. For this, we use the Extensible Markup Language (XML) which is considered as a new standard for data representation and exchange on the Web. XML opens opportunities to develop a new generation of Information Retrieval System (IRS) to improve the interrogation process of document bases on the Web. Our work focuses instead on end-users who do not have expertise in the domain (like a majority of the end-users). This approach supports keyword-based searching like classical IRS and integrates structured searching with the search attributes notion. It is based on an indexing method of document tree leafs which authorize a content-oriented retrieval. The retrieval subdocuments are ranked according to their similarity with the user’s query. We use a similarity measure which is a compromise between two measures: exhaustiveness and specificity.