This chapter explores the foundational role of data management and performance measurement in ensuring long-term well integrity across the full lifecycle of oil and gas wells. The chapter emphasizes that effective integrity management is fundamentally dependent on the availability of accurate, complete, and accessible data spanning design, construction, operation, suspension, and abandonment phases. It details the structure and content of Well Integrity Management Systems (WIMS), highlighting how centralized databases capture essential information—such as barrier schematics, cement logs, test results, corrosion monitoring, and intervention records—for diagnostics, risk assessments, and regulatory compliance. Robust data validation and quality control mechanisms are presented as critical safeguards against erroneous entries, ensuring data consistency, reliability, and auditability. The chapter also outlines a systematic framework for defining and tracking Key Performance Indicators (KPIs), categorized into leading and lagging indicators. These KPIs enable proactive monitoring of well health, identification of emerging risks, benchmarking of performance, and continuous improvement in integrity programs. A tiered structure of KPIs is introduced to balance predictive metrics (e.g., test completion rates, maintenance compliance) with outcome-based indicators (e.g., sustained casing pressure, failure events). Furthermore, this chapter highlights the increasing integration of well integrity data with advanced analytics platforms, laying the groundwork for predictive maintenance and AI/ML-based forecasting of integrity failures. It also identifies persistent challenges—such as data silos, legacy systems, inconsistent formats, and lack of standardization—that impede effective data utilization. Addressing these challenges through digital transformation, organizational accountability, and strategic investment in WIMS tools is essential for building a resilient and future-ready integrity management program. Overall, the chapter positions structured data and KPI frameworks as strategic enablers for safer, more sustainable, and cost-effective well operations.