This book shows the importance of Power Line Communications (PLC) technology to improve and solve the limitations and drawbacks of other communications channels by integrating with these communications channels. Furthermore, PLC technology creates a new hybrid communications channel that can lead to reliable and strong communications systems capable of meeting today's communications challenges for smooth, reliable and high data rate transmission systems able to cope with the challenges facing smart cities. Active researchers on PLC technology contribute to this book by emphasising the importance of this technology in building future smart cities. This book is subdivided into three major thematic parts: Part I: Communications Channels : This part is an overview from a theoretical and a practical perspective presented in the form of survey of the three major communications channels: Power Line Communications (PLC), Visible Light Communications (VLC) and Wireless Communications (WCC) channels. Part II: Hybrid Communications Systems: This part presents examples of how the new emerging technology combines the three communications channels into specific applications. The new hybrid channels are discussed and examples of applications are presented. Part III: PLC and its Applications: This part is reserved for smart homes, smart grid and smart cities, making use of the new hybrid technology with PLC as the backbone.