The reservoir, conduit, and contractile functions of the left atrium are integral to overall cardiac performance. Recent advances in cardiac imaging offer the accurate assessment of LA phasic functions and structure, using techniques such as 3-dimensional echocardiography, color tissue Doppler imaging, and speckle tracking, as well as cardiac computed tomography and magnetic resonance imaging. These new developments are particularly important in view of the increasing use of intervention involving the left atrium. This review article highlights and contrasts the imaging of the size, mechanics, and structure of the left atrium using multiple modalities. The authors discuss recent studies on the clinical applications of the various techniques in disease conditions.