Numerous researchers have employed Csikszentmihalyi's flow theory in their analyses of the behavior of Web users. Flow is a state of consciousness that is experienced by people who are deeply involved in an enjoyable activity such as surfing the Net. The experience is characterized by some common elements such as concentration on the task at hand, a sense of control, a merging of action and awareness, a distorted sense of time, and the autotelic experience, to mention a few. A recognized precondition for flow is that the challenges an individual faces in a particular activity must be matched by the skills he or she uses in meeting those challenges. This paper discusses the roles that challenge and skill play in the flow experiences of Web users.