Landau–Kleffner syndrome (LKS), or acquired epileptiform aphasia, is an epilepsy syndrome (developmental seizure disorder). Children with LKS present with a loss of previously acquired language skills or failure to progress in language development. An additional hallmark of LKS is the seizure pattern associated with it; an abnormally paroxysmal EEG, eventually characterized by electrographic status epilepticus of slow wave sleep (ESES). LKS seizures impact the temporal or parietal-occipital regions of the developing brain. This entry discusses the history, clinical presentation, etiology, differential diagnosis, treatment, and prognosis of LKS. It concludes with a case example of an individual with LKS.