Ultrasound is outstripping other diagnostic imaging techniques in the evaluation of osteoarthritis (OA). Due to its sub-millimetric resolution, ultrasound has the ability to detect minimal morphostructural abnormalities, even from preclinical or asymptomatic disease stages located in the main joint structures predominantly affected by OA: articular cartilage, synovial membrane, and subchondral bone. As of today, ultrasound has proven to be a useful tool for the detection of abnormalities occurring within soft tissues, including synovial hypertrophy, fluid accumulation, and synovial cysts, as well as bony abnormalities, such as osteophyte formation. Additionally, power Doppler signal correlated with histologic evidence of synovial membrane vascularization. In order to describe the ultrasonographic findings of OA, its utility, reliability, and validity as a diagnostic and monitoring tool, a critical review of the literature of hand, hip, and knee OA is provided.