The eLesson Markup Language (eLML) is an open source XML framework for creating structured eLessons using XML. Thanks to a clean separation between content and layout eLML lessons can be transformed into many different formats and layouts. It supports the following output formats: XHTML, IMS Content Package, SCORM, eBooks (ePub format), PDF, LaTeX, Open Document Format (ODF) and DocBook. The framework has been successfully tested with many different LMS like Moodle, OLAT, WebCT/Blackboard and Ilias. A number of tools like the Firedocs eLML Editor to write lessons or the Template Builder to create eLML layout templates are available and help to make eLML one of the best tools to create sustainable e-Learning content.