eXist is an Open Source native XML database featuring efficient, index-based XQuery processing, automatic indexing, extensions for full-text search, XUpdate support and tight integration with existing XML development tools. The database implements the current XQuery 1.0 working draft as of November, 2003 (for the core syntax, some details already following later versions), with the exception of the XML schema related features.

XQuery support in eXist makes it possible to write entire web applications with just XQuery and XSLT. XQuery files can be directly passed to the database, using either the XQueryServlet, the XQueryGenerator for Cocoon or the REST-style API.

Additional features: Java binding, fulltext-search functions, modules in XQuery and Java, extension modules for HTTP support, database manipulation and XSL transformations.

To avoid memory-intensive document tree traversals during query processing, eXist uses an efficient index structure which is based on a numerical indexing scheme for identifying XML nodes in the index. The database is lightweight, completely written in Java and may be easily deployed in a number of ways, running either as a stand-alone server process, inside a servlet-engine or directly embedded into an application.