Ultrasound is a first line examination of the knee and useful diagnostic tool in assessing the various knee lesions. The advantages of ultrasound are that it is non-invasive, easily available at bed side, cheap, well accepted by patients, and that it has technical benefits including dynamic evaluation. Its limitations include reliability, which is largely operator dependent and its inability to evaluate deep structures. Technical guidelines of the ultrasound released by European Society of MusculoSkeletal Radiology (ESSR) and ultrasonographic findings of various knee lesions are described.