In augmented reality (AR), a user can see a virtual world as well as the real world. To avoid registration problems between the virtual world and the real world, the user's viewing pose in both worlds should be kept the same. Fiducial-tracking AR is an attractive approach to the registration problem. However, most of the developed fiducialtracking AR systems have restricted workspaces. To provide a wide range of workspaces (from a small-scale desktop space to a large-scale space) and a wide range of views (from far views to detailed views), an AR system should have scalability. In this paper, we present multiring color fiducial systems and a real-time fiducial detection method for scalable fiducial-tracking AR. We analyze the optimal ring width and develop formulas to obtain the optimal fiducial set with applicationspecific inputs. We develop a real-time ring-detection method that converts the five-DOF ellipse-detection problem to a series of simple steps with a 1-D segmentfilter and multithreshold segmentation. The results lead to a simple and inexpensive means of achieving scalable-area tracking for AR and an approach that is suitable as an optical tracking method for VR as well.