This java applet provides students with opportunities to visualize the Monty Hall paradox (i.e., the famous "three-door" problem often discussed in introductory statistics courses). By going through the simulation and reading the accompanying materials, students can better understand concepts related to probability, and they can also see the need to gather data in order to test theories about what might happen under particular conditions (especially since the outcome of the Monty Hall problem tends to contradict students' initial intuitions).