Event-related potentials (ERPs) are voltage fluctuations of the brain that are time-locked to an objectively definable event. Only part of cerebral electric activities associated with the event are observed as ERPs. Although ERPs may not be the online manifestation of the neural processes that actually operate and transform the event information, the elicitation of a certain ERP component indicates the occurrence of a certain type of information processing in the brain. ERPs can be measured (1) in parallel with a variety of tasks without distorting ongoing cognitive processes and (2) even outside the laboratory using a portable recording system. These merits are especially useful in the field of engineering psychology, whose goal is to understand and predict human cognition and behavior during the interaction with tools, machines, and systems. According to the activity theory which suggests that human mental activities are intrinsically mediated by artifacts, engineering psychology is not only an application-oriented but also a theoretically important area of psychological investigation. The use of ERPs for research topics in engineering psychology was illustrated by examples.