Knee joint is very complex; for many years knee attracted the attention of the best specialists in the world and of many patients. Is commonly said that this articulation is difficult to treat: this was true a few decades ago, where the anatomical knowledge, and then surgery was not as advanced as now. Currently arthroscopic techniques, minimally invasive surgery, more and more knowledge accurate anatomy and physiology of the knee, lead to obtain spectacular recoveries in both sports patients at the highest level, that in patients suffering from osteoarthritis of the knee. In this section we will explain in simple terms all that you would like to know if a patient undergoes a lesion of the meniscus, if you have a problem of knee pain or patellar dislocated kneecap. Or if after a trauma the diagnosis is a cruciate ligament injury or rupture. Older patients who began to suffer from knee arthritis, will find everything about a total knee prosthesis. A chapter on the cartilage of the knee and the grafts is presented.