Shoulder instability is generally diagnosed from a detailed history, physical examination and various radiological studies. Although, a physical examination is essential for making a diagnosis, it is quite difficult. For a precise physical examination, a thorough anatomical knowledge and a great deal of experience is needed. In addition, normal translation and pathologic laxity should be differentiated. An anatomical and biomechanical understanding of a stable and unstable shoulder joint and a precise physical examination are needed to determine the direction and extent of the instability as well as to diagnose the associated lesions and improve the surgical results.