As societies increasingly rely on digital systems, the need for robust strategies to manage cyber threats has become paramount. This chapter introduces the foundational principles of cyber resilience, emphasizing its distinction from, yet complementarity to, traditional cybersecurity and risk assessment. The authors articulate how the rapid expansion of interconnected technologies, from IoT to cloud computing, has expanded the cyber-attack surface and complicated risk quantification. Cyber resilience is defined as the capacity of systems to prepare for, absorb, recover from, and adapt to adverse cyber events, including both known and emergent threats. The chapter outlines the inadequacies of conventional risk models in addressing cascading failures within complex cyber-physical and socio-technical systems. It presents resilience-by-design and resilience-by-intervention paradigms, supported by metrics and model-based assessment tools. Drawing lessons from real-world incidents, including cyber operations during the Russo-Ukrainian War, the chapter illustrates practical applications of resilience strategies such as redundancy, decentralization, and dynamic reconfiguration. By integrating insights from engineering, ecology, and organizational theory, the chapter offers a foundation for understanding and enhancing cyber resilience in critical infrastructure and complex networks.