Considers the relationship between the two independent lines of research into user modelling activities in human-computer interaction (HCI) and artificial intelligence (AI). The paper begins by considering the potential use of AI user models in HCI. The user modelling research conducted in HCI and AI respectively is then discussed along with the goals of HCI and AI. Considerable differences underlie the apparent similarities of the respective research in user modelling in HCI and AI and we discuss these distinctions from the viewpoint of the roles, nature, goals and development of user models. It is argued that HCI can contribute techniques concerned with gathering and modelling user requirements to AI, and in addition a view of how the results of employing AI user models might be evaluated. On the other hand, sophisticated knowledge representation techniques can be provided by AI to the use of embedded user models in HCI.