The perioperative period is a time of profound physiological stress and neurologic vulnerability. Complications such as postoperative delirium, postoperative cognitive dysfunction (POCD), delayed emergence, and intraoperative awareness represent distinct but sometimes overlapping phenomena with important implications for patient safety, satisfaction, and long-term outcomes. Each entity arises from a unique constellation of risk factors and mechanisms, but all share the common thread of altered sensorium and cognition in the perioperative setting. Postoperative delirium is an acute, fluctuating disturbance of attention and awareness that typically develops within hours to days after surgery, particularly in older and frail patients. POCD, in contrast, manifests as longer-lasting deficits in memory, attention, and executive function, often recognized weeks after surgery. Delayed emergence refers to the failure to regain expected levels of consciousness after discontinuation of anesthetics and may reflect residual drug effects, metabolic disturbances, or neurologic injury. Intraoperative awareness, although rare, is psychologically devastating, occurring when patients have explicit recall of surgical events while under general anesthesia. This chapter reviews each condition separately, including definitions, risk factors, pathophysiology, prevention, principles of workup, and management strategies. It also addresses the influence of anesthetic technique on postoperative cognitive outcomes. For internists and perioperative clinicians, recognizing these syndromes is crucial for guiding preventive strategies, collaborating with anesthesiologists, and supporting recovery across the perioperative continuum.