This chapter describes seizure disorder. This chapter is divided into three parts following as epilepsy, newer drugs for focal epilepsy in adults, and diagnosis and management of the epilepsies in adults and children. Epilepsy is a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures, and epileptogenesis is the development of a neuronal network in which spontaneous seizures occur. Epilepsy affects the whole age range from neonates to elderly people, and has varied causes and manifestations, with many distinct seizure types, several identifiable syndromes, but also much that is poorly classified. Epilepsy is a common neurological disorder characterized by recurring epileptic seizures; it is not a single diagnosis but is a symptom with many underlying causes, more accurately termed the epilepsies. Antiepileptic drugs (AEDs) to prevent recurrence of seizures form the mainstay of treatment.