For patients with massive rotator cuff tear and failed total shoulder arthroplasty (TSA), the options are to revise the prosthesis to a customized hemiarthroplasty or to convert to a reverse total shoulder arthroplasty (RTSA). Multiple studies have evaluated the efficacy of these procedures, and although complication rates are higher after revision procedures than after primary arthroplasty, patient outcomes and satisfaction are better after RTSA. This chapter presents a step-by-step guide for successful conversion of failed TSA to RTSA. Rehabilitation protocols and tips for avoiding potential complications and pitfalls are also described.