Completely satisfactory standards for assessing the severity of aortic regurgitation have not yet been formulated. Invasive and noninvasive methodologies have inherent limitations that prevent any single procedure being considered as a gold standard. Nevertheless, Doppler echocardiography, using the full range of imaging modalities, including pulsed-wave and continuous-wave Doppler and Doppler color-flow mapping, may detect and semiquantify the severity of aortic regurgitation with a high degree of accuracy. This article describes the application, methodology, and limitations of the Doppler indices currently used to assess aortic regurgitation.