The Common Land Model (CLM) is a modular land surface model developed by scientists from various institutions to address the need for accurate energy, water, and momentum fluxes across the land-atmosphere interface. The model combines the best features of three existing successful land models: the Land Surface Model (LSM) by Bonan, the Bio-Atmosphere Transfer Scheme (BATS) by Dickinson et al., and the Chinese Academy of Sciences Institute of Atmospheric Physics LSM (IAP94) by Dai and Zeng. CLM is designed to be flexible and modular, allowing easy incorporation of new components and improvements from different groups. It has undergone extensive offline testing using observational data from the Valdai catchment in Russia and the Anglo-Brazilian Amazonian Climate Observation Study (ABRACOS) site in the Brazilian rainforest, demonstrating its ability to simulate key state variables and fluxes accurately. When coupled with the NCAR Community Climate Model (CCM3), CLM significantly improves the simulation of surface air temperature, runoff, and snow mass. The model's modular structure and comprehensive documentation aim to facilitate further development and application in weather forecasting and climate studies.The Common Land Model (CLM) is a modular land surface model developed by scientists from various institutions to address the need for accurate energy, water, and momentum fluxes across the land-atmosphere interface. The model combines the best features of three existing successful land models: the Land Surface Model (LSM) by Bonan, the Bio-Atmosphere Transfer Scheme (BATS) by Dickinson et al., and the Chinese Academy of Sciences Institute of Atmospheric Physics LSM (IAP94) by Dai and Zeng. CLM is designed to be flexible and modular, allowing easy incorporation of new components and improvements from different groups. It has undergone extensive offline testing using observational data from the Valdai catchment in Russia and the Anglo-Brazilian Amazonian Climate Observation Study (ABRACOS) site in the Brazilian rainforest, demonstrating its ability to simulate key state variables and fluxes accurately. When coupled with the NCAR Community Climate Model (CCM3), CLM significantly improves the simulation of surface air temperature, runoff, and snow mass. The model's modular structure and comprehensive documentation aim to facilitate further development and application in weather forecasting and climate studies.