Hi, the current trunk now has support for Python implemented XSLT extension elements. It's sort of a sandbox environment with read-only Elements, where you can do basically anything based on the stylesheet and the input document, and then append some result subtree to the XSLT output tree. Here's a short XSLT snippet that uses an extension, and a Python class that provides such an extension: <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:myns="testns" extension-element-prefixes="myns"> <xsl:template match="a"> <A> <myns:myext><x>X</x><y>Y</y><z/></myns:myext> </A> </xsl:template> </xsl:stylesheet> class MyExt(etree.XSLTExtension): def execute(self, context, self_node, input_node, output_parent): # apply templates to my own children and process the result for child in self_node: for result in self.apply_templates(context, child): if isinstance(result, basestring): el = etree.Element("T") el.text = result else: el = result output_parent.append(el) I don't remember when I first started thinking about this, but it was actually pretty hard to get right until now. I uploaded some docs to the dev site: http://codespeak.net/lxml/dev/xpathxslt.html#extension-elements Note that this is currently an experimental feature that will go into lxml 2.1. Any comments and bug reports will be very much appreciated. Have fun, Stefan