Programming tools, such as JSP and PHP scripts, Java applets, and JavaScript and Shockwave plug-ins, which have become more powerful over recent years, have made possible the development of interactive Web-based exercises. These exercises can simulate various earth science processes and offer instructors unique learning activities for their students. In 1995 we started to build and make available through the Internet activities which focus on the learning and teaching of earth science topics for introductory college and high school courses. These activities, listed in the chronological order of their development, are: Virtual Earthquake, Isochron Dating, Radiocarbon Dating, River Discharge, and River Flooding. As the programming tools became more robust over time, we’ve been able to provide each subsequently developed activity with greater interactivity, enabling the student user to make careful observations and measurements, do simple calculations, and answer questions as they progress through the exercise. To provide instructors with a permanent record, a personalized and printable "Certificate of Completion" is awarded to each student at the satisfactory completion of each activity. This “virtual courseware” is widely used. During Spring quarter of 2002, these exercises were successfully completed by approximately 110,000 college and high school students from nearly 450 colleges and high schools. To date, in excess of one million students have completed at least one of these activities. Various assessments of these activities and the voluntary feedback from approximately 1000 instructors has been positive over the years. Generally, instructors seek more similar on-line activities as enhancements to teaching and learning. A complete revision of Virtual Earthquake is now available with many new features and a built-in assessment tool for learning outcomes. Additional activities about global warming, biodiversity, population growth, and groundwater are being developed. These materials can be accessed at http://sciencecourseware.com