For over 30 years, the Doppler effect has been used to identify blood flow with ultrasound. Many Doppler techniques are currently available, including continuous-wave Doppler, pulsed Doppler, color Doppler, and power Doppler. Each Doppler technique has strengths and limitations. Color Doppler provides a survey of blood flow in real time, which has improved our ability to detect and characterize vascular abnormalities throughout the body. However, to use the information provided by color Doppler and to help ensure accurate diagnosis, it is necessary to understand the basic principles of Doppler image interpretation thoroughly. In addition, to maximize the information obtained, it is important to adjust technical parameters to optimize the Doppler image. This article focuses on the basic concepts necessary to produce high-quality color Doppler images and to interpret those images accurately.