Instability of the shoulder can be classified as uni- or multidirectional with or without general hyperlaxity. Instability of a shoulder without hyperlaxity is often caused by a single traumatic event for the unidirectional instability and by two or several different events for the rarer multidirectional instability. The diagnosis of unidirectional instability is made with a positive apprehension test. For multidirectional instabilities, the anterior and posterior apprehension tests are positive. The treatment consists of surgical repair of the labrum-capsule complex for both the uni- and the multidirectional instabilities without hyperlaxity. For shoulders with a concomitant hyperlaxity, uni- or multidirectional instability is often caused by only minor trauma. Hyperlaxity itself is not a disease but represents a risk factor of instability. The typical feature of hyperlaxity is the positive "sulcus sign". Unidirectional instability with hyperlaxity is characterised by a positive apprehension test combined with a positive sulcus sign. Multidirectionally unstable shoulders with hyperlaxity have a positive anterior and posterior apprehension test as well as a positive sulcus sign. The unidirectional instability with hyperlaxity is best treated surgically whereas conservative treatment is recommended for the multidirectional instability with hyperlaxity. The voluntary instability without loss of control of position of the shoulder is not a real instability and has an excellent prognosis without treatment.