The Agricultural Production Systems Simulator (APSIM) is a modular modeling framework developed by the Agricultural Production Systems Research Unit in Australia. It simulates biophysical processes in farming systems, focusing on economic and ecological outcomes of management practices under climatic risk. APSIM includes modules for crops, pastures, and trees, soil processes such as water balance, nutrient transformations, soil pH, erosion, and management controls. The framework supports data input and output, user interfaces for model construction and application, and visualization tools. APSIM has been applied in various contexts, including on-farm decision-making, farming systems design, climate forecasting, supply chain analysis, waste management, risk assessment, and research and education. It has been tested in diverse systems and environments, demonstrating its robustness and applicability. The model's performance is supported by extensive testing and application studies, which are detailed in the paper.The Agricultural Production Systems Simulator (APSIM) is a modular modeling framework developed by the Agricultural Production Systems Research Unit in Australia. It simulates biophysical processes in farming systems, focusing on economic and ecological outcomes of management practices under climatic risk. APSIM includes modules for crops, pastures, and trees, soil processes such as water balance, nutrient transformations, soil pH, erosion, and management controls. The framework supports data input and output, user interfaces for model construction and application, and visualization tools. APSIM has been applied in various contexts, including on-farm decision-making, farming systems design, climate forecasting, supply chain analysis, waste management, risk assessment, and research and education. It has been tested in diverse systems and environments, demonstrating its robustness and applicability. The model's performance is supported by extensive testing and application studies, which are detailed in the paper.