RELAX NG is a book written by Eric van der Vlist for O'Reilly and submitted to an open review process. The result of this work is freely available on the World Wide Web under a Free Documentation Licence (FDL).

The subject of this book, RELAX NG (http://relaxng.org), is a XML schema language developped by the OASIS RELAX NG Technical Committee and recently accepted as Draft International Standard 19757-2 by the Document Description and Processing Languages subcommittee (DSDL) of the ISO/IEC Joint Technical Committee 1 (ISO/IEC JTC 1/SC 34/WG 1).