Electroencephalography is the oldest functional imaging technique in continued use by psychiatry and neurology. Although lacking the spatial resolution of newer imaging techniques, it retains an exceptionally high degree of temporal resolution, as electroencephalographic (EEG) recordings reflect brain activity essentially on the same time scale as the activity of cortical neurons. Electroencephalography has traditionally been used to assist diagnosis of epilepsy, delirium, and gross neuropathology. Although no qualitatively specific EEG markers exist for psychopathology, the electroencephalogram is highly sensitive to a variety of neuropathological conditions. In addition, the introduction of quantitative EEG analysis has greatly expanded the usefulness of the technique in the evaluation of dementia and delirium. Quantitative electroencephalography has been an important research tool, showing promise for enhancing our understanding of the neurophysiology and neuropathology underlying these conditions (Cook and Leuchter 1996; Holschneider and Leuchter 1999; Knott et al. 2001). The APA Task Force on Quantitative Electrophysiological Assessment (1991) suggested that the technique has particular clinical utility for detection of slow-wave abnormalities.