Epilepsy is a complex neurological disease, characterized by the propensity for ongoing unprovoked seizures as well by an array of neurocognitive, behavioral and social impairments. Seizures can be classified into those with generalized, focal or unknown onset. The etiology of epilepsy is variable ranging and includes underlying genetic, structural – metabolic and unknown causes. Over the last decades, The International League Against Epilepsy has played a pivotal role in reframing how we define and classify epilepsy. Throughout this chapter, we explore the definition of epilepsy and its etiologies as well as its underlying pathophysiology and briefly discuss management options. The underlying mechanisms for seizure development are discussed as well as the genetics of epilepsy. Importantly, we discuss several of the epilepsy syndromes throughout this chapter, which have their onset from the neonatal period to adolescence, and describe their key clinical features, treatment and prognosis.