Manifestation of musculoskeletal infection in children depends on the developmental anatomy of bones and in particular its changing vascular supply. Thus, it is essential to understand this process thoroughly. Osteomyelitis, septic arthritis, and cellulitis are relatively common. There are three accepted stages of osteomyelitisacute, subacute, and chronic. Each has a unique presentation and imaging appearance, but they can be confused with other entities. Radiology, ultrasound, nuclear imaging, CT, and MRI each play a critical role depending on the clinical scenario and the suspected pathogen. Much of this discussion focuses on common bacterial infections (including methicillin-resistant Staphylococcus aureus ), but meningococcemia, tuberculosis, fungal infections, and syphilis are also discussed. In addition, the chapter presents manifestations of osteomyelitis in unique locations, such as the epiphysis, the pelvis, and the spine, and in unique patient populations, such as those with sickle-cell disease. Although chronic recurrent multifocal osteomyelitis is auto-infl ammatory rather than infectious, we include it here as well.