This paper focuses on the use of the World Wide Web (WWW) to support classroom-based education. Drawing from experiences in five undergraduate and graduate level courses, we describe three ways that the WWW can be applied in the classroom. First, the WWW can be used to introduce a greater variety of information into the classroom. Second, it can directly support classroom activities. Third, the WWW makes it possible to share more information, techniques, and materials among instructors. We then consider the costs and benefits, for both the instructors and the students, of these three uses of the WWW. Finally, we discuss challenges and opportunities for instructors and researchers interested in the use of the WWW in the classroom.