Storage and retrieval of XML documents is an interesting and important subject. The techniques and research results discussed in this chapter prove this to be a very big challenge. Several reasons may cause the technological clash that has been produced by the rise of XML and the necessity of storing XML documents. First, file-based storage techniques are too weak; second, research on semi-structured data is not so well known. Furthermore, the widespread database management techniques barely fit, and finally, the requirements of the XML data management systems have not been fully explored. Therefore, we should not miss the opportunity to develop either new storage techniques for the known database systems or even new database management systems, like the native XML data management systems. They could lead to a totally new awareness of the definition and usage of data and documents.