This book provides a comprehensive review of the models and approaches that can be employed to simulate modular multilevel converters (MMCs). Each solution is described in terms of operating principle, fields of applicability, advantages, and limitations. In addition, this work proposes a novel and efficient simulation approach for MMCs based on sub-circuit isomorphism. This technique, which has its roots in the electronics fields, can be profitably exploited to simulate MMCs regardless of the model used to describe its sub-modules, including the most accurate ones. Lastly, this book considers a well-known high voltage direct current (HVDC) benchmark system consisting of two MMCs. After describing the implementation details of each benchmark component, simulation results in several scenarios (ranging from normal operating conditions to faults in the AC and DC grid) are included to validate the proposed approach and showcase its key features. Due to its educational content, this book constitutes a useful guide for PhD students and researchers interested in the topic of MMCs and their simulation. It also serves as a starting platform for junior electrical engineers who work in the field of power electronic converters for HVDC systems.