Electroencephalography is the most practical and accessible neuroimaging technique. An abnormal pattern of asymmetric activity in the frontal regions due to relative hyperactivity over the right and/or relative hypoactivity over the left frontal regions has been demonstrated in the electroencephalographic studies of depression. Alterations in brain functional cortical connectivity in resting-state networks and a loss of selectivity in resting functional connectivity were detected in an electroencephalographic study of major depressive disorder. Researchers suggested that several electroencephalography-based methods may be useful biological marker for predicting antidepressant response. Alpha- and theta-band EEG abnormalities, the combined Antidepressant Response Index(ATR), cordance, EEG source localization have the potential to offer predictors of treatment response. Future studies will be needed to validate their usefulness for clinical practice.