One of the key activities in telerobotic and emerging virtual environment systems is mechanical interaction with objects. In normal human experience, mechanical (or haptic) interaction is one of the most expressive ways in which one can effect changes in the environment. How one can and should build suitable haptic interfaces (gloves, joysticks, exo-skeletons, etc.) is currently a subject of intense research throughout the world. Given that haptic interface design is severely limited by available technology, critical choices between complexity and performance must be made. Ultimately these choices must be made with knowledge of task complexity and the required fidelity of display. This presentation will review the current state of haptic interface technology, attempt to classify the important performance attributes, and try to give a sense of the design challenges which lie ahead.