Ultrasound imaging has been utilized as a useful diagnostic tool in medicine and biology. It can offer real-time, non-radiative, and functional imaging in the visualization of internal body structures. In particular, various ultrasound techniques have been applied to diagnose skin diseases in dermatology. In this chapter, after the basic principles of ultrasound are introduced, ultrasound imaging systems, including ultrasound transducers, are demonstrated. Also, various applications of current ultrasound imaging techniques such as high-frequency ultrasound, ultrasound elastographic, and quantitative ultrasound imaging in the diagnosis of skin lesions are demonstrated in detail.