The clinical application of musculoskeletal ultrasonography in rheumatology started with the use in early diagnosis of patients with rheumatoid arthritis, and now its role has expanded to evaluation of other common rheumatic diseases such as spondyloarthritis and crystal-associated arthropathy (i.e., gout and calcium pyrophosphate deposition disease). Introduction of high-frequency probes and power Doppler has enabled highly sensitive and reliable evaluation of a patient's condition and disease processes. Ultrasonographic assessments subsequently have become one of the important outcome measures in clinical studies, and its usefulness has been recognized in daily clinical practice. Ultrasonography is useful in early and differential diagnosis of inflammatory arthritis, and its property should be well adapted to evaluation of disease activity. Many data have proven that it is more sensitive and reliable than physical examination, and it can describe subtle pathology that cannot be detected by conventional radiography. Though further progress towards standardization of the technique and development of a consensus in scoring methods is needed, it is expected that ultrasonography will not only improve clinical outcomes but also contribute to gaining more insight into rheumatic diseases.