Anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis represents one of the most prevalent forms of autoimmune encephalitis, characterized by the production of antibodies against NMDA receptors in the brain. This disorder has gained significant recognition since its formal identification in 2007, fundamentally changing our understanding of autoimmune neuropsychiatric conditions. The clinical presentation typically involves a complex constellation of symptoms including acute psychiatric manifestations, seizures, movement disorders, autonomic instability, and altered consciousness, often progressing through distinct phases. The condition predominantly affects young adults and children, with a notable association with ovarian teratomas in female patients, though approximately half of the cases occur without detectable tumors. Diagnosis relies on the detection of anti-NMDAR antibodies in cerebrospinal fluid or serum, supported by characteristic clinical features, electroencephalogram, and neuroimaging findings. Treatment involves a multimodal approach combining tumor removal when present, immunosuppressive therapy, and comprehensive supportive care. While the majority of patients experience favorable outcomes with appropriate treatment, early recognition and intervention are critical for optimal recovery. This chapter provides a comprehensive examination of anti-NMDAR encephalitis, encompassing its pathophysiology, clinical manifestations, diagnostic approaches, therapeutic strategies, and prognostic factors, serving as a valuable resource for clinicians managing this complex but increasingly treatable condition.