As the elderly population increases, so will the number of surgical patients with dementia and other cognitive disorders. Laboratory evidence suggests that some commonly used anaesthetic agents may accelerate the Alzheimer’s disease (AD) process, but robust clinical research is still needed. This chapter discusses the need for peri-operative guidelines for patients with dementia, and the many opportunities for further research to inform such guidelines. It also covers postoperative delirium and its association with longer hospital and intensive care unit stays, cognitive decline after surgery, and higher mortality. Finally, it covers postoperative cognitive dysfunction (POCD), how standardized definitions and study methodology are lacking, and that studying cognitive trajectory after anaesthesia and surgery is often confounded by various clinical elements that cannot be accounted for methodologically.