The paper introduces the aerosol-climate model ECHAM5-HAM, which is based on a flexible microphysical approach and minimizes externally imposed parameters. The model predicts the evolution of an ensemble of internally and externally mixed aerosol populations, their size distribution, and composition. The size distribution is represented by a superposition of log-normal modes, and the major global aerosol compounds (sulfate, black carbon, particulate organic matter, sea salt, and mineral dust) are included. The model's performance is evaluated against in-situ and remote sensing measurements, showing good agreement with global aerosol system observations. The simulated global annual mean aerosol optical depth (AOD) is in excellent agreement with estimates from AERONET and MODIS-MISR satellite retrievals. The model's ability to reproduce the main patterns of AOD attributable to anthropogenic activity is also highlighted. The paper discusses the model's setup, including the ECHAM5 general circulation model, the modal concept, emission module, chemistry module, deposition module, relative humidity, aerosol microphysics module M7, and radiation module. The results section presents simulations for the year 2000, comparing the model's emissions, budgets, and lifetimes with previous studies.The paper introduces the aerosol-climate model ECHAM5-HAM, which is based on a flexible microphysical approach and minimizes externally imposed parameters. The model predicts the evolution of an ensemble of internally and externally mixed aerosol populations, their size distribution, and composition. The size distribution is represented by a superposition of log-normal modes, and the major global aerosol compounds (sulfate, black carbon, particulate organic matter, sea salt, and mineral dust) are included. The model's performance is evaluated against in-situ and remote sensing measurements, showing good agreement with global aerosol system observations. The simulated global annual mean aerosol optical depth (AOD) is in excellent agreement with estimates from AERONET and MODIS-MISR satellite retrievals. The model's ability to reproduce the main patterns of AOD attributable to anthropogenic activity is also highlighted. The paper discusses the model's setup, including the ECHAM5 general circulation model, the modal concept, emission module, chemistry module, deposition module, relative humidity, aerosol microphysics module M7, and radiation module. The results section presents simulations for the year 2000, comparing the model's emissions, budgets, and lifetimes with previous studies.