Shoulder instability is defined as the abnormal motion of the humeral head in relation to the glenoid, that is accompanied by pain and discomfort. Normal stability is due to a balance of active musculature and static shoulder constraints. Static stabilizers include the labrum, glenohumeral (GH) ligaments, capsule and rotator interval, whereas dynamic constraints include the rotator cuff and scapular musculature. Considering these things, the authors undertook the present review to consolidate the current literature on shoulder anatomy and anatomical variation as it relates to instability.