Brachial plexus injuries, particularly those affecting the upper roots (C5–C6), often result in severe shoulder dysfunction, notably loss of abduction and external rotation. These injuries are common in young, active individuals and primarily result from high-energy trauma, such as motorcycle accidents. Among different surgical techniques, spinal accessory nerve (SAN) transfer to the suprascapular nerve (SSN) is a widely used technique to restore shoulder function. This procedure involves transferring the SAN while preserving trapezius function by carefully selecting the division point distal to its first or second branches. The goal is to achieve a tension-free, direct end-to-end transfer, facilitating optimal reinnervation of the supraspinatus and infraspinatus muscles. This chapter explores the anatomical considerations, diagnostics studies, surgical techniques, recent advancements in SAN to SSN transfer, and the rehabilitation process, emphasizing its role in improving outcomes for patients with upper brachial plexus injuries.