The shoulder joint is a ball-and-socket joint, also known as the glenohumeral joint. It is formed by the articulation between the head of the humerus and the glenoid cavity of the scapula. The shoulder joint is one of the most mobile joints in the human body, allowing for a wide range of motion. It is also the most unstable joint in the body due to the amount of motion it allows. The shoulder joint is surrounded by a joint capsule, which is a fluid-filled sac that lubricates the joint and is made up of ligaments.