This paper suggests that a way to the new generation of powerful E-learning systems starts on the crossroads of two emerging fields: courseware re-use and adaptive educational systems. The paper presents the KnowledgeTree, a framework for adaptive E-learning based on distributed re-usable learning activities currently under development. The goal of KnowledgeTree is to bridge the gap between the information power of modern educational material repositories and the just-in-time delivery and personalization power of intelligent tutoring systems (ITS) and adaptive hypermedia (AH) technologies. (Contains 27 references.) (Author)