Doppler ultrasound is widely used in clinical settings for measurement of blood flow dynamics and tissue motion. The continuous-wave Doppler method enables measurement of very fast blood flow such as that caused by heart valve occlusion, while it lacks spatial resolution. In measurement of blood flow, ultrasonic echoes from blood cells are much weaker than those from slowly moving tissues such as the heart wall. Therefore, a filter, i.e., clutter filter, is required to suppress echoes from slowly moving tissues. The pulsed-wave Doppler method enables measurement of blood flow or tissue motion in a specific region assigned by a so-called “range gate”. However, maximum measurable velocity is determined by the aliasing effect. The aliasing phenomenon is also explained in this paper. Color Doppler ultrasound estimates velocity of a target using the autocorrelation technique, and it can visualize two- or three-dimensional distribution of blood flow or tissue velocity. This paper provides brief explanations on the basic principles for measurement of blood and tissue velocities based on the Doppler ultrasound.