In this paper we describe our own experience in preparing animated presentations of computer science concepts with Leonardo Web, a Java-based animation system that we have previously developed. Our discussion is aimed at highlighting how different visualization tools and techniques turned out to be useful in realizing effective Web-based teaching material. Our experience culminated in the preparation of an on-line repository of animated illustrations for a textbook on algorithms and data structures edited by McGraw-Hill in 2004. © Springer-Verlag Berlin Heidelberg 2005