The thoracodorsal nerve (TDN) is the second most frequently reported collateral brachial plexus (BP) branch, following the medial pectoral nerve (MPN), which can be used as an infraclavicular intraplexal donor for restoring elbow flexion through reinnervation of the musculocutaneous nerve (MCN) in partial BP injuries. Compared to the MPN, the TDN provides a superior axonal load, significantly greater length, and a more suitable diameter match with the MCN, facilitating tension-free, direct nerve coaptation. However, the TDN is less often viable in partial BP injuries, especially involving the C7 root, and it may lead to loss of the latissimus dorsi muscle as a potential donor for muscle-tendon transfer. Therefore, careful intraoperative evaluation is crucial to determine TDN over MPN donor suitability. This chapter outlines the anatomical and technical aspects of TDN-MCN transfer, and discuss the controversies, problems, and possible solutions based on personal experiences and published research.