Clinical electrophysiology offers a variety of powerful and informative methods by which to study cerebral function and dysfunction after traumatic brain injury (TBI). Electroencephalography (EEG) was the first clinical diagnostic tool to provide evidence of abnormal brain function caused by TBI (Glaser and Sjaardema 1940; Jasper et al. 1940; Williams 1941). Such early observations led to the development of increasingly sophisticated clinical and research electrophysiological techniques, including quantitative EEG (QEEG), topographic EEG (also known as brain electrical activity mapping, or BEAM), evoked potentials (EPs), and event-related potentials (ERPs), magnetoencephalography (MEG), and magnetic source imaging (MSI). These techniques permit noninvasive measurement of brain activity with temporal resolution superior to that of other functional neuroimaging methods, including positron emission tomography, single-photon emission computed tomography (SPECT), and functional magnetic resonance imaging. However, and as discussed later in this chapter, the gains in temporal resolution offered by these techniques are accompanied by relative losses in spatial resolution (at least when compared with that afforded by functional neuroimaging).