It is well known that artifacts can be observed during US examinations; the same is true also for Doppler and color-Doppler images of blood flow. Recognizing these artifacts is important to avoid image misinterpretations and, when possible, to overcome them by modifying either techniques or unit settings, or both. This work was aimed at presenting the several artifacts which can be observed during Doppler investigations, at classifying them, and trying to understand the physical and/or technical principles underlying their origin. Doppler and color-Doppler artifacts can be divided into four large groups: 1) artifacts regarding evaluation of the presence of flow; 2) artifacts regarding evaluation of the direction of flow; 3) artifacts regarding determination of the velocity of flow; 4) artifacts affecting spatial location, on the screen, of the examined vessel. Each of the above can cause severe diagnostic misinterpretations, if not correctly recognized and interpreted. It must be kept in mind that an accurate analysis of unit settings during scanning, and the meticulous evaluation of the obtained color images are of the utmost importance for the proper use of this valuable but difficult diagnostic technique.