We review our recent work on the development and evaluation of three-dimensional electrocardiographic imaging technology (3DEIT). Cardiac electrophysiological properties, including activation time and transmembrane potentials, are estimated from body surface ECG signals with the aid of a realistic geometry heart model in which electrophysiological a priori information is incorporated. We have conducted computer simulation studies to demonstrate the feasibility of imaging activation sequence throughout the three-dimensional myocardium, and localizing sites of origin of activation and arrhythmias using our 3DEIT approach. We will also review the pilot experimental studies in evaluating the 3DEIT approach in a patient with pacemaker and experimental animals with intracardiac recordings. Our promising results to date suggest the feasibility of the 3DEIT technology that we are developing and that it merits further investigation.