This chapter focuses on the principles of conventional Electroencephalography (EEG) recording and interpretation and the typical applications of EEG to the assessment of persons with neurological and psychiatric conditions. The electrical activity measured at the scalp with EEG is generated by cerebral cortical neurons underlying the scalp where the recording electrodes are placed. The electrical activity recorded during EEG by pairs of electrodes (channels) is displayed by arranging those channels into specific sets. The two main categories of EEG abnormalities are: slowing or the presence of slower frequency waveforms than what should be present, and epileptiform discharges, or specific EEG waveforms that signify cortical hyper-irritability and an increased risk for clinical seizures. The EEG is commonly used in clinical assessment of Behavioral Neurology & Neuropsychiatry (BN&NP) patients. Triphasic waves usually arise from a diffusely abnormally slow background, and are a classic EEG abnormality associated with metabolic encephalopathy.