The aerosol-climate model ECHAM5-HAM is introduced, which uses a flexible microphysical approach to simulate the evolution of internally and externally mixed aerosol populations, their size-distribution, and composition. The model includes major global aerosol compounds such as sulfate, black carbon, particulate organic matter, sea salt, and mineral dust. Simulated global annual mean aerosol burdens for the year 2000 are: sulfate (0.80 Tg(S)), black carbon (0.11 Tg), particulate organic matter (0.99 Tg), sea salt (10.5 Tg), and mineral dust (8.28 Tg). The model results are in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is 0.14, in excellent agreement with AERONET and MODIS-MISR measurements. The model reproduces main patterns of AOD attributable to anthropogenic activity. The model is based on a flexible microphysical approach, allowing the application in a wide range of climate regimes. The aerosol size-distribution is represented by a superposition of log-normal modes. The model includes a detailed treatment of aerosol dynamics, including coagulation, condensation, and nucleation. The model also incorporates a chemistry module for the sulfur cycle, a deposition module for dry and wet deposition, and a radiation module for aerosol optical properties. The model is computationally efficient and allows long-term climate simulations. The model is evaluated against in-situ and remote sensing measurements, showing good agreement with observations. The model results are compared with other studies, showing that the simulated aerosol burdens and lifetimes are in the range of previous estimates. The model is able to reproduce the main patterns of aerosol distribution and their radiative effects. The model is flexible and can be extended to include more compounds. The model is a valuable tool for studying aerosol-climate interactions and their feedback processes.The aerosol-climate model ECHAM5-HAM is introduced, which uses a flexible microphysical approach to simulate the evolution of internally and externally mixed aerosol populations, their size-distribution, and composition. The model includes major global aerosol compounds such as sulfate, black carbon, particulate organic matter, sea salt, and mineral dust. Simulated global annual mean aerosol burdens for the year 2000 are: sulfate (0.80 Tg(S)), black carbon (0.11 Tg), particulate organic matter (0.99 Tg), sea salt (10.5 Tg), and mineral dust (8.28 Tg). The model results are in good agreement with observations of the global aerosol system. The simulated global annual mean aerosol optical depth (AOD) is 0.14, in excellent agreement with AERONET and MODIS-MISR measurements. The model reproduces main patterns of AOD attributable to anthropogenic activity. The model is based on a flexible microphysical approach, allowing the application in a wide range of climate regimes. The aerosol size-distribution is represented by a superposition of log-normal modes. The model includes a detailed treatment of aerosol dynamics, including coagulation, condensation, and nucleation. The model also incorporates a chemistry module for the sulfur cycle, a deposition module for dry and wet deposition, and a radiation module for aerosol optical properties. The model is computationally efficient and allows long-term climate simulations. The model is evaluated against in-situ and remote sensing measurements, showing good agreement with observations. The model results are compared with other studies, showing that the simulated aerosol burdens and lifetimes are in the range of previous estimates. The model is able to reproduce the main patterns of aerosol distribution and their radiative effects. The model is flexible and can be extended to include more compounds. The model is a valuable tool for studying aerosol-climate interactions and their feedback processes.