This book comprehensively examines the communication challenges posted  by regulating large-scale flexible loads  These challenges include high access demands, explosive data volume, frequent data transmission, realistic performance-based impact analysis, and security concerns. Addressing these issues is very important for the advancement of modern power systems, since large-scale flexible loads are becoming contributing resources for the regulation purposes. This book has been written to solve these issues. At the beginning of this book, the architecture of communication networks is introduced to specify the challenges of regulating large-scale flexible loads. The interconnection of power and communication networks is reviewed to emphasize the potential applications of advanced ICTs. Part I introduces the planning and operation approaches of communication networks for the control of large-scale flexible loads. Part II analyses the impact of communication latency and detection errors on dispatching flexible loads. Part III discusses the security of communication networks for the regulation of large-scale flexible loads from a data protection perspective. Finally, the book reviews current research and introduces the prospective work on emergency communication resource in resilient modern power systems.