Outcome assessment has become a cornerstone of contemporary spine surgery, reflecting a paradigm shift from surgeon-centered metrics toward patient-centered evaluation of pain, function, and quality of life. In lumbar spine disorders, traditional radiographic and neurological outcomes often demonstrate limited correlation with symptom burden and disability, necessitating the systematic use of standardized outcome instruments. This chapter reviews the evolution of outcome metrics in spine surgery, with emphasis on clinician-reported outcomes, patient-reported outcome measures (PROMs), and large-scale registry data. Widely used disease-specific instruments such as the Oswestry Disability Index and Neck Disability Index are discussed alongside generic health-related quality-of-life measures and contemporary systems including the Patient-Reported Outcomes Measurement Information System. Key concepts related to interpretation of PROMs such as responsiveness, minimal clinically important difference, substantial clinical benefit, and patient acceptable symptom state are summarized, highlighting their relevance to clinical decision-making and outcome benchmarking. The role of national and international spine registries in generating real-world evidence, facilitating quality improvement, and informing value-based spine care is examined, with attention to both their strengths and methodological limitations. Challenges associated with implementation of standardized outcome assessment across diverse healthcare settings are also considered. Collectively, these frameworks underscore the central role of outcome science in advancing evidence-based, patient-focused spine care.