This article helps designers of Web-based science instruction construct analogies that are as effective as those used in classrooms by exemplary science teachers. First, the authors explain what analogies are, how analogies foster learning, and what form analogies should take. Second, they discuss science teachers' use of analogies. Third, they examine examples of Websites that use analogies to explain science concepts. Finally, the authors provide guidelines for using analogies effectively in Web-based science instruction. (Contains 4 figures and 1 table.)