Enterprise-scale modernization has evolved from a strategic option to an operational imperative in the contemporary digital economy. Organizations that continue to rely on legacy applications and rigid, hardware-centric network infrastructures face mounting challenges in sustaining competitiveness, operational efficiency, and security resilience. Rapid technological innovation, evolving customer expectations, intensifying cloud-native competition, and increasingly sophisticated cyber threats are collectively reshaping the enterprise IT landscape. Systems originally designed for stability and centralized control now struggle to support modern requirements such as real-time analytics, elastic scalability, distributed workforce enablement, continuous deployment cycles, and AI-driven automation. As a result, modernization initiatives are becoming foundational to long-term enterprise sustainability and growth.This review provides a comprehensive examination of enterprise modernization strategies across both application and network domains. On the application side, modernization approaches such as cloud migration, microservices adoption, API-first design, containerization, DevOps integration, and Infrastructure as Code (IaC) are analyzed for their impact on scalability, agility, and maintainability. Transitioning from monolithic architectures to modular, loosely coupled systems enables organizations to accelerate innovation cycles, improve fault isolation, and enhance operational efficiency. Simultaneously, adopting cloud-native frameworks facilitates resource elasticity, cost optimization, and global service delivery.From a networking perspective, the paper explores the transformation from traditional perimeter-based infrastructures to software-defined networking (SDN), software-defined wide area networking (SD-WAN), and Zero Trust security architectures. These paradigms introduce centralized control, programmable network policies, identity-based access enforcement, and continuous monitoring capabilities. By decoupling control and data planes and embedding security mechanisms directly into network layers, enterprises can enhance visibility, reduce lateral threat movement, and support distributed cloud environments.Furthermore, the review evaluates automation-driven infrastructure and AI-enabled operations (AIOps) as critical enablers of modernization at scale. Automated provisioning, predictive monitoring, anomaly detection, and self-healing systems reduce operational complexity while improving service reliability. Governance frameworks, compliance integration, risk mitigation strategies, and cultural transformation are also discussed as essential components of successful modernization initiatives.The paper highlights both the tangible benefits—such as improved agility, cost reduction, resilience, and competitive advantage—and the inherent technical and organizational challenges associated with modernization, including data migration complexity, legacy integration risks, skill gaps, and change resistance. Finally, emerging trends such as AI-native architectures, edge computing integration, 5G-enabled connectivity, platform engineering, and sustainable green IT practices are examined as shaping forces of next-generation enterprise IT ecosystems.Overall, enterprise-scale modernization is framed not merely as a technological transition but as a strategic, organizational transformation that redefines how enterprises design, secure, deploy, and manage digital systems in an increasingly complex and interconnected world.