Primary mitral regurgitation (MR) is the first cause of valvular regurgitation in Western countries. Echocardiography is the cornerstone for diagnosing MR and more specifically for establishing its aetiology and mechanism, for quantifying its severity, progression, and repercussion and for assessing the likelihood of successful of valve repair. Two-dimensional/three-dimensional transthoracic and transoesophageal echocardiography are the most widely used methods. Interest is growing for exercise echocardiography particularly in patients in whom symptoms do not correlate well with MR severity and for risk stratification. The experience of multi-slice computed tomography in primary MR is still limited. Conversely, cardiovascular magnetic resonance has gained progressive relevance and represents the alternative method of choice.