In psychiatric literature, several terms including sundowning, sundowning syndrome, and nocturnal delirium have been used interchangeably to describe the same observations. The reason for this confusion is the lack of a clear and precise definition for the observed phenomenon along with indefinite sources of etiology. Sundowning is a descriptive term for observed behaviors, rather than a psychiatric diagnosis as defined in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition-text revision (DSM-IV-TR). This article by Kim and colleagues reviews past investigations to characterize the observed phenomenon of sun downing. It also reviews the theories of etiology and the current approaches to sundowning treatment and management.