Acute bacterial meningitis is a life-threatening infection. By definition, meningitis is an infection of the meninges and the subarachnoid space. Bacterial meningitis is associated with an inflammatory response that involves the meninges, the subarachnoid space, the brain parenchyma, and the cerebral arteries and veins. As such, bacterial meningoencephalitis is the more accurate descriptive term. This chapter discusses the epidemiology, etiology, pathophysiology and pathogenesis, diagnosis, differential diagnosis, treatment, complications, and prognosis of the disease. The discussion of diagnosis covers clinical manifestations, physical examination findings, laboratory tests, and imaging studies. The discussion of treatment covers empirical therapy, specific antimicrobial therapy, and dexamethasone therapy. Graphs compare causative organisms and clinical manifestations of community-acquired meningitis. Illustrations depict proper patient positioning for detecting nuchal rigidity, Kernig sign, Brudzinski sign, and lumbar puncture, as well as a sagittal view of a lumbar puncture needle as it is advanced into the subarachnoid space. An algorithm delineates the approach to the patient with symptoms and signs of bacterial meningitis. Tables outline bacterial pathogens based on predisposing and associated conditions, cerebrospinal fluid diagnostic studies for meningitis, the appearance of the organism on a Gram stain, empirical antimicrobial therapy based on predisposing and associated conditions, recommendations for specific antibiotic therapy in bacterial meningitis, and recommended doses for antibiotics commonly used in the treatment of bacterial meningitis. This review contains 8 highly rendered figures, 6 tables, and 75 references.