Fog computing is an emerging paradigm in the field of distributed computing that acts as an extension of cloud computing. Unlike the traditional cloud model, which relies on centralized data centres located far from the end users, fog computing brings computation, storage, and networking services closer to the physical location of data sources and users. This proximity to end devices significantly reduces communication latency, enhances data processing speed, and supports real-time decision-making, which is critical in applications that demand immediate responses, such as autonomous vehicles, healthcare monitoring, and industrial automation.Fog computing is a paradigm that extends cloud computing to the edge of the network, aiming to reduce latency, enhance scalability, and provide better support for real-time applications. This text book outlines the foundational principles, system architecture, and diverse application areas of fog computing.