Understanding the location and magnitude of glenoid bone loss is extremely important at the time of both primary and revision shoulder arthroplasty. Specific patterns of glenoid bone loss have been described for primary glenohumeral osteoarthritis, cuff tear arthropathy, inflammatory arthritis, and failed shoulder arthroplasty. Although radiographs are useful in planning arthroplasty procedures, CT has become the imaging modality of choice to evaluate and classify bone loss before shoulder arthroplasty. Two-dimensional images may be used to measure various angles and calculate areas of bone loss. Software programs for preoperative planning or navigation provide alternative assessment modalities. Evaluation of glenoid bone loss and subluxation may help surgeons plan for anatomic or reverse arthroplasty and anticipate the potential need for bone graft or augmented components. Although understanding of glenoid bone loss at the time of arthroplasty has improved substantially, further research is needed to understand optimal targets for version, inclination, and joint line position, as well as to determine the best surgical techniques to manage areas of glenoid bone deficiency.