It is generally recognized that information systems are becoming more complex and, therefore, intelligent user interfaces are needed to improve user interaction with these systems. Furthermore, the exponential growth of the Internet makes it difficult for the users to cope with the huge amount of available on-line information. The challenge that information providers and system engineers face is the creation of adaptive (Webbased) applications, as well as the development of “personalized” retrieval and filtering mechanisms. Responses to this challenge come from various disciplines including machine learning and data mining, intelligent agents and multi-agent systems, intelligent tutoring, information retrieval, etc.