a | According to the International League Against Epilepsy 2017 basic seizure classification, which is intended for use by practitioners not specializing in epilepsy, epileptic seizures can be classified as focal onset, generalized onset or unknown onset. When possible, focal seizures are divided into seizures with preserved awareness or with impaired awareness. Focal aware seizures were previously referred to as simple partial seizures, and focal impaired awareness seizures were previously referred to as complex partial seizures. Focal-onset, generalized-onset and unknown-onset seizures can include motor and non-motor forms. Focal seizures include seizures that progress to bilateral tonic–clonic seizures (formerly referred to as secondarily generalized tonic–clonic seizures). This classification also distinguishes between bilateral seizures (which propagate to both hemispheres) and generalized seizures (which originate simultaneously in both hemispheres). b | The expanded seizure classification is intended for use by clinicians with expertise in the diagnosis and treatment of epilepsy. This classification has a structure similar to that of the basic classification, but the motor and non-motor categories are further divided according to features that might be present during seizures, such as automatisms and myoclonus. Adapted with permission from Ref. 2, John Wiley & Sons.