lxml is copyright Infrae and distributed under the BSD license (see doc/licenses/BSD.txt), with the following exceptions: Some code, such a selftest.py, selftest2.py and src/lxml/_elementpath.py are derived from ElementTree and cElementTree. See doc/licenses/elementtree.txt for the license text. lxml.cssselect and lxml.html are copyright Ian Bicking and distributed under the BSD license (see doc/licenses/BSD.txt). test.py, the test-runner script, is GPL and copyright Shuttleworth Foundation. See doc/licenses/GPL.txt. It is believed the unchanged inclusion of test.py to run the unit test suite falls under the "aggregation" clause of the GPL and thus does not affect the license of the rest of the package. The isoschematron implementation uses several XSL and RelaxNG resources: * The (XML syntax) RelaxNG schema for schematron, copyright International Organization for Standardization (see src/lxml/isoschematron/resources/rng/iso-schematron.rng for the license text) * The skeleton iso-schematron-xlt1 pure-xslt schematron implementation xsl stylesheets, copyright Rick Jelliffe and Academia Sinica Computing Center, Taiwan (see the xsl files here for the license text: src/lxml/isoschematron/resources/xsl/iso-schematron-xslt1/) * The xsd/rng schema schematron extraction xsl transformations are unlicensed and copyright the respective authors as noted (see src/lxml/isoschematron/resources/xsl/RNG2Schtrn.xsl and src/lxml/isoschematron/resources/xsl/XSD2Schtrn.xsl)