癫痫（英语：Epilepsy，英文词源来自古希腊文中的动词「ἐπιλαμβάνειν」,意为「抓住、持有，或折磨」），或称脑痫、羊痫、羊癫疯、羊角风、猪脚疯、发羊吊，音译伊比力斯症，是一种长期性神经系统疾患，以癫痫抽搐发作为特征。这些抽搐发作形式很多，有些可以是非常短暂且几乎无法察觉，也可以是长时间的剧烈抽动。癫痫的抽搐往往反复发作而并无直接起因，由特殊原因引起的抽搐则不被认为是癫痫。

虽然有些癫痫病例由脑部外伤、中风、脑肿瘤、服毒或酗酒等病因导致，但大多数癫痫发病并无已知病因。癫痫抽搐发作是由于大脑皮质神经细胞活动过度或异常的结果。 诊断癫痫通常需要排除其他能引起类似症状的疾患（如晕厥），并查找是否有直接发病因素存在。癫痫通常可以以脑电图（EEG）确诊。

Epilepsy is a group of neurological diseases characterized by epileptic seizures. Epileptic seizures are episodes that can vary from brief and nearly undetectable to long periods of vigorous shaking. These episodes can result in physical injuries including occasionally broken bones. In epilepsy, seizures tend to recur, and have no immediate underlying cause. Isolated seizures that are provoked by a specific cause such as poisoning are not deemed to represent epilepsy. People with epilepsy in some areas of the world experience stigma due to the condition.