The Global Land Data Assimilation System (GLDAS) is a powerful tool developed by scientists from NASA's Goddard Space Flight Center and NOAA's National Centers for Environmental Prediction. It integrates advanced observing systems to improve forecast model initialization and hydrometeorological investigations. GLDAS uses ground- and space-based observations to constrain land surface models (LSMs) and data assimilation techniques to correct biases in atmospheric model-based forcing. The system supports three LSMs: Mosaic, Noah, and the Community Land Model (CLM). GLDAS employs innovative data assimilation methods, including ensemble and extended Kalman filters, to integrate observation-based data products from multiple sources. It provides high-resolution, offline terrestrial modeling of land surface states and fluxes in near-real time. The system's output is freely available for scientific research, education, policy-making, and hazard planning. Validation and intercomparison of various forcing data options are ongoing, and GLDAS is being tested for initializing weather and climate prediction models.The Global Land Data Assimilation System (GLDAS) is a powerful tool developed by scientists from NASA's Goddard Space Flight Center and NOAA's National Centers for Environmental Prediction. It integrates advanced observing systems to improve forecast model initialization and hydrometeorological investigations. GLDAS uses ground- and space-based observations to constrain land surface models (LSMs) and data assimilation techniques to correct biases in atmospheric model-based forcing. The system supports three LSMs: Mosaic, Noah, and the Community Land Model (CLM). GLDAS employs innovative data assimilation methods, including ensemble and extended Kalman filters, to integrate observation-based data products from multiple sources. It provides high-resolution, offline terrestrial modeling of land surface states and fluxes in near-real time. The system's output is freely available for scientific research, education, policy-making, and hazard planning. Validation and intercomparison of various forcing data options are ongoing, and GLDAS is being tested for initializing weather and climate prediction models.