This paper presents research and development of an adaptive World Wide Web-based system called Explor@ Advisory Agent, capable of tailoring advice to the individual student's needs, actions, and reactions toward pedagogical events, as well as according to diagnosis of content acquisition. Explor@ Advisory Agent consists of two sub-systems, the Advice Editor and the Student Advisor. The Advice Editor allows course designers to enter the instructional structure, as well as the content structure, in the form of a hierarchical tree, tagging corresponding pages, as well as entering rules (conditions and operations) for how and when advice is to appear. The Student Advisor displays the student's progression through the two structures by indicating what is achieved or completed. The system traces the student's progression according to knowledge acquisition through questions, questionnaires, and rules on a test, and according to how the student navigates through the instructional material. In this manner, the student modeling relies on both the overlay and diagnostic modeling techniques. Future research aims at introducing peer or team collaboration and assistance by allowing the agent to match learners' progress by displaying the progression bars, if the learner chooses to participate. (Contains 32 references.) (Author/MES)