The study of conceptual models is both a complex and an important field within the HCI domain. Many of its key principles resulted from research and thinking carried out in the 1980s, arguably in the wake of Norman (1983). Since then, the importance of conceptual models in affecting the usability of an Information and Communication Technology (ICT) system has become well-established (e.g., they feature prominently in the widely cited design guidelines for interfaces defined by Norman , which are summarized in Figure 1 by Lienard ). Today, most HCI professionals are able to attribute significant meaning to the term conceptual model and to recognize its importance in aiding usability. However, two problems seem to prevail. First, some HCI researchers and practitioners lack a precise understanding of conceptual models (and related ideas), and how they affect usability. Second, much of the research in this field is (necessarily) abstract in nature. In other words, the study of conceptual models is itself highly conceptual, with the result that practitioners may find some of the theory difficult to apply. This article is designed to help both researchers and practitioners to better understand the nature of conceptual models and their role in affecting usability. This includes explaining and critiquing both contemporary and (possible) future approaches to leveraging conceptual models in the pursuit of improved usability.