The quality of HMI in automation is an important issue in manufacturing. This special form of interaction occurs when the combination of human abilities and machine features are necessary in order to perform the tasks in manufacturing. Balint (1995) has identified three categories of such human-machine systems: 1. Machines might do the job without human involvement, but the feasibility is questionable. For example, weld seams in car assembly are made mostly autonomously by robots, but in many cases, humans have to guide the robot to the weld point, because the robot is not able to locate the point correctly, which is a relatively easy task for a human. 2. Humans might do the job without machines, but the efficiency/reliability is questionable. This is the case in almost all cases of automation (e.g., the varnishing of cars). 3. HMI is necessary (no purely machine- or human-based execution is possible), although robots today are widely in use; in many cases, they cannot substitute humans completely, because the possible conflicts that can occur are so diverse that a robot alone cannot manage them. The term HMI is used widely for the interaction of a human and a somewhat artificial, automated facility, which is true in many situations, including HCI. In this article, we speak of HMI in industrial settings. We term the machine especially for industrial facilities for producing a certain (physical) output; in this case, the term man-machine interaction also is used synonymously for HMI. We define HMI as the relation between a human operator and one or more machines via an interface for embracing the functions of machine handling, programming, simulation, maintenance, diagnosis, and initialization.