Science teachers face challenges that affect the quality of instruction. Tight budgets, limited resources, school schedules, and other obstacles limit students' opportunities to experience science that is visual and interactive. Incorporating web-based Java applets into science instruction offers a practical solution to these challenges. The applets described in this article are more than mere animations. While animations can enhance instruction, they lack an interactive component. This article advocates the use of applets that allow the user to make one or more manipulations and observe the response. Therefore, when visiting websites that advertise applets, teachers must be sure to discriminate between those that allow manipulations and those that do not.