Echocardiography, also known as cardiac ultrasonography, is the most commonly used noninvasive cardiac imaging modality. It provides real-time images of the heart and comprehensive information regarding the cardiac structure, function, and hemodynamics. This chapter will discuss the general concept, brief history, and basic physics of cardiac ultrasound, types of transducers, echocardiography modes, principles of Doppler echocardiography, and Doppler-based hemodynamic formulas in a simple and targeted format.