T o date, most human–computer interactive systems have focused primarily on the graphical rendering of visual information and, to a less- er extent, on the display of auditory information. Among all senses, the human haptic system provides unique and bidirectional communication between humans and their physical environment. Extending the frontier of human–machine interaction, haptic interfaces—or force feedback devices—have the potential to increase the quality and capability of human–computer interaction by exploiting our sense of touch and ability to skillfully manipulate objects. The direct physical interaction with computer-generated objects enabled by haptic interfaces provides a useful and intuitive augmentation to visual display and the opportunity to enhance the under- standing of, and interaction with, complex data sets. Several novel applications already effectively use haptic technologies; these include molecular docking, nano- material manipulation, surgical training, virtual proto- typing, and digital sculpting. Compared to visual and auditory display, haptic ren- dering has extremely demanding computational requirements. To maintain a stable system while dis- playing smooth and realistic forces and torques, haptic update rates of 1 kHz or more are typical. Haptics pre- sents new challenges in the development of novel data structures to encode shape and material properties, as well as new techniques for data processing, analysis, physical modeling, and visualization. This special issue examines some of the latest advances on haptic render- ing and applications, and provides an introductory view of the challenges and opportunities in the field. This issue The first article, a tutorial by Salisbury, Barbagli, and Conti, provides an overview of the haptics field with a particular focus on the architecture of haptic rendering systems and the devices that enable force feedback- based haptic interaction. Unlike graphic and auditory rendering, the rendering of haptic interactions requires modeling the physical interactions between objects and generating forces that arise during contact and motion in real time. As in the field of computer graphics, prac- titioners of computer haptics are intensely interested in the best rendering methods of objects, so that humans can meaningfully perceive them. This topic alone is a vast area that will occupy researchers for years to come. The first article gives a basic view of methods used to render the way an object feels—it discusses modeling these physical interactions and the dynamic stability issues that arise in real-world implementations. In the design of haptic systems, we need to consider the sensory, perceptual, and cognitive abilities and lim- itations of humans. In the second article, Hale and Stan- ney present a review of physiological and psychophysical aspects of human cutaneous and kinesthetic senses, fol- lowed by a discussion of issues related to incorporating haptic interaction with a graphical display. The authors present several design guidelines for developing multi- modal interaction systems. Their objectives were to iden- tify conditions under which haptic interaction might enhance human perception and performance. By com- bining neurological and behavioral research methods, they evaluate various sensory integration methods (for example, ramp-up patterns or timing) for better design of haptic interaction systems. A key area in haptics receiving increased attention is the rendering of surface texture. Surface texture typi- cally refers to microgeometric features on object sur- faces in haptic rendering. Intrinsic surface properties like textures are among the most salient haptic charac- teristics of objects. The third article by Choi and Tan pre- sents a survey on systematic studies of issues that contribute to the perceived instability of haptic texture rendering. The authors conduct psychophysical exper- iments to investigate conditions under which perceived instability of virtual texture occurs and the type of per- ceived instability frequently reported by users. By ana- lyzing the measured data, they identify the proximal stimuli that caused the perceived instability and indi- cate the sources that produce the stimuli. The next article by Mahvash and Hayward describes an efficient method to synthesize the nonlinear haptic response of deformable models from prerecorded sim- Guest Editors’ Introduction Ming Lin University of North Carolina, Chapel Hill Kenneth Salisbury Stanford University Haptic Rendering— Beyond Visual Computing 22 March/April 2004 Published by the IEEE Computer Society 0272-1716/04/$20.00 © 2004 IEEE