This chapter provides a classification of spondylolisthesis at the L5-S1 level that can help guide surgeons with respect to management strategy, incorporating older concepts in addition to more recent concepts surrounding spino-pelvic balance. Spondylolisthesis occurs most commonly at the L5-S1 level, and management can involve a spectrum of interventions that include conservative treatment, instrumentation and fusion without reduction of the spondylolisthesis, and reduction with spinal realignment that includes instrumentation and fusion. A similar suggestion was made in the Mac-Thiong et al. publication that also concluded surgical reduction for high-grade spondylolisthesis patients with postural instability as defined by lumbosacral deformity. The chapter also provides insight for the decision-making process that preceded the classification system created by the Spinal Deformity Study Group. It describes that differences exist in the spondylolisthesis patient that largely have to do with whether the pelvis is balanced or unbalanced. The chapter suggests that reduction techniques were likely best reserved for the unbalanced subgroup.