Recent advancements in carbon and molecular electronics have opened the door to a new generation of electronic nanoscale components. This book outlines the basic principles of electromagnetic-based communication at this nanoscale using terahertz and optical frequencies with a focus on theoretical principles and applications. It answers the questions: How can nano-devices communicate with each other by applying electromagnetic techniques? Do conventional communication and networking schemes and principles still apply? How feasible is it to deploy such networks with various applications?