The functional separation of different system components has been used to address some critical challenges in architecture design. One of the well-known approaches of physical separation of functional units is in client–server architectures. The server side of this separation is hidden inside the cloud infrastructure in the case of an Internet scale system. This model is serving a wide range of applications running over the Internet providing storage, computing power, and redundant services for reliability. However, in the new paradigm of the Internet-of-Things (IoT), the traditional separation partly fails to meet the set of system requirements. Fog computing is introduced as an intermediate layer between the clients and the Cloud. It brings computing, storage, management, and network services, among others, closer to the sensor/actuator nodes. This book discusses the features of Fog computing, its advantages, internal details, and present case studies to demonstrate it in real application scenarios. The focus of this chapter is to give an overview of Fog computing at a higher level.