This prospective, multicenter longitudinal five-year study of X-STOP PEEK implant usage in LSS patients is designed to supplement pre-market safety and effectiveness data with information on longer-term device performance in a population of patients with moderately impaired physical function at preoperative baseline (i.e., an "indicated" population) who elect to undergo X-STOP PEEK surgery. This post-approval study will enroll 240 patients at up to 8 clinical sites where all participating spine surgeons have completed a company-sponsored physician training program. The clinical sites recruited to participate in this study comprise a geographically diverse mix of academic, referral, and/or community based sites.