Lower trapezius tendon transfer with Achilles tendon allograft augmentation may be used to treat patients with lack of active external rotation following shoulder paralysis or massive irreparable posterosuperior rotator cuff tears. In the setting of shoulder paralysis, the integrity of the ipsilateral lower trapezius may be compromised. In this instance, the contralateral lower trapezius may be used with reasonable results. In the setting of irreparable rotator cuff tears, the procedure may be performed through an open or arthroscopically assisted technique. The latter avoids the need for an acromial osteotomy and risk of nonunion associated with repair of the osteotomy. Both are effective in reversing pseudoparesis or pseudoparalysis. Advanced degenerative changes have an effect on outcomes, resulting in less pain improvement, decreased range of motion, and greater need for reoperation with conversion to reverse total shoulder arthroplasty. Nonetheless, the lower trapezius tendon transfer is an effective option for restoring active external rotation with relatively consistent results.