Proximal junctional kyphosis (PJK) remains one of the most challenging complications following long-segment spinal fusion in adult spinal deformity (ASD) surgery, with reported incidence rates of 20–40%. Ligamentoplasty, an emerging technique for creating a “soft landing” at the upper instrumented vertebra (UIV), offers a biomechanical transition zone to mitigate the abrupt rigidity change that predisposes patients to PJK. This chapter presents the rationale, surgical technique, and clinical outcomes of posterior ligamentoplasty using autologous fascia lata or synthetic substitutes. We describe a standardized approach for patient selection, preoperative planning, and step-by-step surgical implementation. Early clinical studies demonstrate promising reductions in PJK rates, with 2-year follow-up data showing decreased proximal junctional angle progression and lower revision surgery rates. Ligamentoplasty represents a valuable addition to the surgical armamentarium for addressing the challenging problem of junctional failure in ASD surgery.