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? Topics covered include an introduction to nano-communication; fundamentals and applications of nano-electromagnetic communications; simulation and experimental platforms for nano-electromagnetic communication networks; terahertz antenna design for wearable applications; terahertz application in food contamination detection; channel modelling for electromagnetic nano-communication; modulation, coding and synchronization techniques for nano-electromagnetic communications in the terahertz band; routing protocols for nano-electromagnetic communication networks; error control mechanisms for nano-electromagnetic communication networks; and conclusion and future outlook.