Doppler ultrasound is routinely used in the clinical setting to evaluate blood flow in many major vessels of the body. Spectral Doppler is used to display the normal and abnormal signature waveforms that are unique to each vessel. It is important for the sonographer and the radiologist to recognize both what is normal and what is abnormal in a spectral Doppler display. In this review, we briefly explain the physics behind Doppler ultrasound and some of the most common mathematical equations applied in a routine clinical examination. We also describe and demonstrate normal versus abnormal spectral Doppler signature waveforms of vessels in the neck, abdomen, pelvis, and fetus.