The development of large-scale renewable generation and load electrification call for highly efficient and flexible electric power integration, transmission and interconnection. High Voltage DC (HVDC) transmission technology has been recognized as the key technology for this scenario. HVDC transmissions, including both the line commutated converter (LCC) HVDC and voltage source converter (VSC) HVDC have played an important role in the modern electric power system. However, with the inclusion of power electronic devices, HVDC introduces the characteristics of nonlinearity and different timescales into the traditional electromechanical system and thus careful modeling and simulation of HVDC transmission are essential for power system design, commissioning, operation and maintenance. This book focuses on the modeling and simulation of HVDC transmission systems. The development of HVDC technologies is briefly introduced, and then the role of modeling and simulation in the research and development of HVDC systems is discussed. The chapters cover the general practice of HVDC modeling and simulation; electromagnetic modeling of LCC HVDC; VSC HVDC system modeling and stability analysis; electromagnetic modeling of DC grids; electromagnetic simulation of HVDC transmission; electromechanical transient simulation of LCC HVDC; electromechanical simulation of VSC HVDC; dynamic phasor modeling of HVDC; small-signal modeling of HVDC systems; hybrid simulation for HVDC; and real-time modeling and simulation for HVDC systems. The simulation algorithms are explained for each model and case studies and application examples are included. This book is essential reading for engineers and researchers involved with transmission grid construction, as well as advanced students of electrical engineering.