The event-related potential (ERP) is a major methodological tool used to investigate the functioning of the cerebral cortex of humans and other mammalian species. The cerebral cortex is the part of the mammalian brain that is most critical for sensory perception, motor action, and cognition. The ERP yields vital information about neuronal population activity in the cortex in relation to sensory, motor, or cognitive events. The temporal resolution of the ERP is ideally suited for capturing the timing of neurophysiological processes in the cortex, and hence it provides a sensitive electrophysiological signature of neurocognitive activity. In fact, the ERP is the principal recording methodology currently in use for investigating the fine temporal structure of human cognitive processing. Like the closely linked event-related magnetic field, the ERP can be recorded noninvasively, and is thus of great value for the study of cognition in normal human subjects. The ERP is also valuable in the clinical setting for determining the temporal integrity of cortical processes in neurological patients. First, this chapter discusses the neurophysiological origins of the cortical ERP. Next, the different techniques by which the ERP is measured, and the many forms that it takes, are examined. Finally, the ways in which the ERP is modeled, and the procedures by which it is analyzed, are described.