Déjà vu experiences are common in normal subjects. In addition, they are established symptoms of temporal lobe seizures. The author argues that the phenomenon is the result of faulty and isolated activity of a recognition memory system that consists of the parahippocampal gyrus and its neocortical connections. This memory system is responsible for judgments of familiarity. The result is that a momentary perceived scene is given the characteristics of familiarity that normally accompany a conscious recollection. The normal functioning of other brain structures involved in memory retrieval--the prefrontal cortex and the hippocampus proper--leads to the perplexing phenomenological quality of déjà vu. The hypothesis accounts for many characteristics of déjà vu in healthy subjects and is well fitting with experimental findings in patients with epilepsy.