An abnormal clinical event that occurs with a set of signs and symptoms different from baseline activity originating from the cortex of the brain is a seizure. During this event, the EEG shows a corresponding electrographic change. The seizure semiology (seizure depiction) represents the cortical region of epileptic activity. The homunculus is a type of map used to correlate the cortical location of seizure activity to patient movements. EEG electrodes placed on the scalp represent certain areas of the underlying cortex. In this way, the electrodes show us where the abnormal cortical signals likely originate. Using this schema, we can reasonably deduce where the seizure activity originates and propagates. However, detecting seizures and distinguishing seizure events can be challenging. This chapter will discuss how seizures are defined, the interictal-ictal continuum, and status epilepticus.