The exponential growth of digital infrastructure has rendered data centers a critical backbone of contemporary society, facilitating cloud computing, big data analytics, and digital services. However, this growth is accompanied by significant energy consumption, operational costs, and environmental impacts, making energy efficiency and sustainability urgent priorities. This research article presents a comprehensive examination of data center energy use, metrics for assessing energy performance, and methodological frameworks for sustainable operations. Drawing on extensive empirical studies and theoretical models, including recalibrated energy estimates (Masanet et al., 2020) and performance metrics for green data centers (Reddy et al., 2017), this study analyzes the conceptual and operational underpinnings of energy efficiency. We evaluate established and emerging frameworks such as Power Usage Effectiveness (PUE) and Data Center Infrastructure Efficiency (DCiE), integrating them with holistic resource productivity indices (Haas et al., 2008; Brocklehurst, 2021). The article provides an in-depth discussion of key performance indicators (KPIs) for software and hardware optimization (Fatima et al., 2024), architectural tactics for sustainable cloud deployment (Vos et al., 2022), and metrics for multi-level green performance (Schödwell et al., 2012). Limitations of current approaches, including inconsistencies in metric standardization and data reporting, are critically analyzed, and strategies for bridging these gaps through integrated frameworks are proposed. The study underscores the necessity of combining technological, operational, and policy-oriented approaches to achieve energy-efficient and environmentally sustainable data centers. Findings indicate that adopting a multi-dimensional energy efficiency framework not only reduces operational energy demand but also aligns with global sustainability goals, thereby enhancing the long-term resilience of digital infrastructure.