Accurate evaluation of mitral regurgitation (MR) severity remains a challenging task in clinical cardiology. The importance of proper quantification of regurgitation cannot be underestimated because a delayed decision to replace or repair a defective valve may lead to worsening ventricular function and increased perioperative and long-term mortality. In this review we discuss both recent developments in the quantification of MR as well as new insights into the pathophysiology and progression of this lesion.