XML has become a standard format in information exchange and integration. Database support of persistent data storage and query capability is often desired for many XML applications. While it is possible to store XML data in traditional relational databases or object-oriented databases, we also desire high-performance native XML databases that are particularly tailored for XML data. We believe an ideal XML database needs to be generic, automatic, access transparent and performance transparent. With these features as the fundamental success criteria for XML databases, this thesis discusses various existing XML database solutions. With these features as design goals, we develop a native XML database that includes native XML storage and an implementation of the XQuery language. This native database is generic in the sense that it accepts any well-formed XML data, regardless of the actual structure of data, and does not rely on schema existence. This database system is automatic because it does not require any database physical design works. Retrieving XML documents or fragments is solely through the XQuery interface. Query performance is transparent with respect to the structure of data.