The advancement of computer and networking technologies are providing a diverse means to support learning in a more personalized, flexible, portable, and on-demand manner. In order to improve the learning process for all students (with different pre-knowledge, personal characteristics and preferred learning styles), adaptability is introduced to already established and newly developed eCourses. However, the process of creating and applying (semi-)adaptive eCourses must be supported by a suitable software solution that would make the development of all the resources/activities such advanced eCourses should include (adaptive eLessons, various sorts of tests and assignments, etc.) flexible, yet simple enough to be performed by all teachers. This thesis is the result of the implementation of such an environment. The author advocates why adaptability is useful in eLessons, offering the possibilities for its implementation by using and extending Moodle, an Open Source eLearning platform.