The growing interest in the field of educational technology in the design of constructivist learning environments has led to a renewed examination of problem-based learning (PBL), an approach to instruction in which all learning results from students' efforts to solve a complex problem. Concurrent advances in technology make it possible to use this approach with a wider range of audiences than have traditionally used PBL, yet few guidelines exist for designers interested in creating computer-based PBL environments. This paper presents some of the lessons learned from the process of developing Alien Rescue, winner of the 2001 Learning Software Design Competition sponsored by the University of Minnesota. (Author)