A seizure is characterized by abnormal and excessive electrical brain activity that disrupts the normal brain function. Seizures are heterogeneous and diagnosed clinically, but the electroencephalogram (EEG) is the foremost diagnostic tool. If an episode is captured during an EEG, it is usually obvious whether it was a seizure or another paroxysmal event. If the event in question was a seizure, the EEG can also reveal the seizure onset. For purely electrographic or nonconvulsive seizures, which are commonly encountered in neonates and critically ill patients, the EEG may actually be the only way to diagnose seizures. EEG abnormalities between seizures can also be informative, suggesting the seizure’s etiology and onset. This chapter reviews the electrographic findings in common epilepsy syndromes. After diagnosing a patient with seizures, the physician should next aim to classify the seizure type, starting with determining whether the onset is focal or generalized, and then etiology.