This chapter describes Web-based instructional tutors that support active and engaging learning. Towards that end, a theoretical foundation for designing such tutors is proposed and two Web-based tutors described. The tutors reason about a student’s knowledge and their own teaching strategies while taking advantage of the possibilities of the Web, by being open to other resources (Web sites) and other people (online communities). One tutor, Rashi, provides problem-based activities and tracks a student’s critical thinking in biology and geology, and the second, iMANIC, uses hypermedia to customize online lectures for individual students based on learning need. This work provides promising data points for the development of authentic and effective learning that can take advantage of the possibilities of the Web, without being rooted in extensions of what already exists in the classroom, such as lectures or bulletin boards.