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. There have been attempts to provide a classification scheme as a tool for the surgeon to better identify how to decide upon the various management options. Several studies have been published demonstrating the complexity of a spondylolisthesis at the L5-S1 level; several of these studies highlight that the slip alone is not the only factor that should be considered in the management of these patients. 1 Previous attempts at classifications had poor interobserver reliability; therefore, they were not adapted. The purpose of this article is to provide 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 on this topic.