Septic arthritis is an inflammatory condition within the joint in reaction to bacterial infection in the joint space. Emergent diagnosis and initiation of therapy are necessary to prevent joint destruction and, in some cases, serious systemic illness. This review covers the epidemiology, assessment and stabilization, diagnosis, treatment and disposition, and outcomes of septic arthritis. Figures show the pathophysiology of bone infection; an algorithm for the initial evaluation and management of a suspected septic joint; a magnetic resonance image of vertebral body osteomyelitis; a cutaneous sinus in a patient with underlying chronic posttraumatic osteomyelitis at the site of a previous tibial fracture; the probe-to-bone test for diagnosing osteomyelitis in the diabetic foot; an algorithm for the initial evaluation and management of suspected vertebral body osteomyelitis; nonsurgical treatment of osteomyelitis of the foot in a patient with diabetes; and algorithms for the evaluation and management of osteomyelitis in diabetic patients with neuropathic ulcers and no or mild foot infection, osteomyelitis in diabetic patients with neuropathic ulcers and moderate or severe foot infection, and chronic posttraumatic osteomyelitis. Tables list supportive findings for diagnosis of chronic osteomyelitis, risk factors for the development of septic arthritis in patients with underlying joint disease, microbiology in septic arthritis, empirical antibiotic therapy for septic arthritis, microbiology in vertebral osteomyelitis, antibiotic therapy for vertebral osteomyelitis awaiting culture results, representative studies with likelihood ratios for diagnostic tests used in the evaluation of native joint septic arthritis, antibiotic therapy for vertebral osteomyelitis with unknown or established microbiology, and antibiotic therapy for diabetic pedal osteomyelitis with unknown or established microbiology. Key words: osteomyelitis, probe-to-bone test, septic arthritis, septic joint, vertebral osteomyelitis This review contains 10 highly rendered figures, 9 tables, and 110 references.