EEG is very sensitive to changes in neuronal function resulting from ischemia. The authors briefly review essentials of EEG generation and the effects of ischemia on the underlying neuronal processes. They discuss the differential sensitivity of various neuronal processes to energy limitations, including synaptic disturbances. The clinical applications reviewed include continuous EEG monitoring during carotid surgery and acute ischemic stroke, and EEG monitoring for prognostication after cardiac arrest.