The use of ultrasound in rheumatology practices is steadily increasing. This imaging modality not only is cost-effective but also serves as a valuable diagnostic tool for rheumatic conditions, offering guidance for interventions and monitoring treatment progress. Owing to its acceptable levels of diagnostic sensitivity and specificity in inflammatory rheumatic disorders, ultrasound is a reliable option. While MRI is often considered the gold standard for musculoskeletal diagnosis, a recent study has shown that ultrasound is nearly as effective in diagnosing synovitis, bone erosion, bursitis, tendinitis, tenosynovitis, enthesitis, meniscal lesions, osteophytes, synovial effusion, synovial hypertrophy, crystal deposition, etc. This chapter explores the use of ultrasound as an outcome measurement instrument in rheumatology.