A decline in cognitive function is a frequent complication after major surgery. Postoperative cognitive impairments have generally been divided into short (postoperative delirium) and long-term disturbances (postoperative cognitive dysfunction [POCD]). Long-term impairments are often subtle and overlooked. They need to be objectively assessed with neuropsychological tests in order to be diagnosed. Although POCD has been the subject of considerable research over the past decades, it remains uncertain why some patients do not return to preoperative levels of cognitive function. Surgery and anesthesia have both been implicated in playing a role in developing POCD, and certain patient-related factors, such as advanced age and low preoperative baseline cognitive function have consistently been found to predict postoperative cognitive decline. This article will provide an overview of POCD, and its etiology, and provide advice on possible strategies on preventing it.