Increasing knowledge of instability in the shoulder has created a more complex evaluation sequence. The history continues to be important. Many physical examination maneuvers are available to further define the problem. Routine roentgenographic examination has been extended to include views specifically designed to demonstrate subtle bony changes. Complex radiographic contrast studies, especially computed arthrotomography, can confirm most anatomic lesions. When surgical treatment is under consideration, reexamination under anesthesia is increasingly being recognized as an important, essential procedure. Arthroscopy will effectively identify pathologic lesions within the joint and confirm uncertain diagnoses. An organized sequence of examinations is necessary for a thorough clinical investigation. After the investigation is complete, a classification of the shoulder instability can be made that relates to the results of treatment. The classification includes the elements of etiology, volition, direction of instability, and degree of instability.