Musculoskeletal infections are common, and the delay between diagnosis and treatment is the most important determinant of outcome. Ultrasound (US) is a widely available imaging modality that can be used quickly for the assessment of cellulitis, abscess, septic bursitis, tenosynovitis, arthritis, and osteomyelitis. Identification of the causative micro-organism is essential for diagnosis and to establish optimal treatment. Because of its multiplanar and real-time imaging capability, US is the technique of choice to guide needle aspiration of any suspicious fluid collection, abscess, synovial sheath, bursa, or joint for microbial analysis. Because the imaging is not degraded by metal artifact, US is an excellent modality for imaging infectious processes around orthopedic hardware.