Septic arthritis is an important medical emergency, with high morbidity and mortality. We review the changing epidemiology of infectious arthritis, which incidence seems to be increasing due to several factors. We discuss various different risk factors for development of septic arthritis and examine host factors, bacterial proteins and enzymes described to be essential for the pathogenesis of septic arthritis. Diagnosis of disease should be making by an experienced clinician and it is almost based on clinical symptoms, a detailed history, a careful examination and test results. Treatment of septic arthritis should include prompt removal of purulent synovial fluid and needle aspiration. There is little evidence on which to base the choice and duration of antibiotic therapy, but treatment should be based on the presence of risk factors and the likelihood of the organism involved, patient’s age and results of Gram’s stain. Furthermore, we revised joint and bone infections due to tuberculosis and atypical mycobacteria, with a special mention of tuberculosis associated with anti-TNFα and biologic agents.