Ultrasound has been used as a diagnostic tool for more than 40 years. Many medical applications have adopted ultrasound, mostly notably in obstetrics and cardiology. Started by a few scientists and clinicians in different parts of the world in the early 1950s, it did not become an established diagnostic tool until the early 1970s when grayscale ultrasonography was introduced. Modern ultrasound scanners are capable of producing images of anatomical structures in great detail in grayscale and of blood flow in color in real-time. State-of-the-art four-dimensional scanners that yield three-dimensional volumetric images in real-time are pushing the present technical capability to its limit. Ultrasound is currently the second-most used clinical imaging modality after conventional X-ray radiography. Although ultrasound is considered to be a mature technology, technical advances are constantly being made. The most significant achievements in ultrasound recently have been the developments of approaches capable of the quantitative measurement of tissue elastic properties, namely ultrasound elastography and radiation-force imaging, high-frequency imaging yielding improved spatial resolution, and therapeutic applications in drug delivery and high-intensity focused ultrasound surgery. The miniaturization of scanners has become a trend. In this paper, the history and current state of medical ultrasound are reviewed and future developments are discussed.