Robert Siegfried presents a framework for efficient agent-based modeling and simulation of complex systems. He compares different approaches for describing the structure and dynamics of agent-based models in detail. Based on this evaluation, the author introduces the General Reference Model for Agent-based Modeling and Simulation (GRAMS). Furthermore, he presents parallel and distributed simulation approaches for the execution of agent-based models, from small scale to very large scale. The author shows how agent-based models may be executed by different simulation engines that utilize underlying hardware resources in an optimized fashion.