This work is a U.S. government work and is not protected by U.S. copyright law. It is published under the Public Domain Mark 1.0. The MODIS Aerosol Algorithm, Products, and Validation paper describes the development and evaluation of satellite algorithms for retrieving aerosol properties from NASA's Terra and Aqua satellites. The MODIS sensor provides daily global observations across a wide spectral range, enabling the derivation of aerosol optical thickness and size parameters over land and ocean. The paper details the aerosol products available, including optical thickness at multiple wavelengths, effective radius, and mass concentration. Validation against two years of AERONET data from 132 stations shows that MODIS optical thickness retrievals have uncertainties of ±0.03–0.05τ over ocean and ±0.05–0.15τ over land. The effective radius retrievals have an uncertainty of ±0.11 μm. The MODIS aerosol retrieval algorithm is described for both land and ocean, with the land algorithm using calibrated reflectances and cloud masks to identify and process aerosol data. The ocean algorithm includes cloud and sediment masking, and uses a lookup table to derive aerosol optical thickness, effective radius, and other parameters. The paper also discusses the validation of aerosol products, including comparisons with AERONET data, and highlights the accuracy and reliability of MODIS aerosol retrievals for climate studies. The MODIS aerosol products are available at various levels, with level 2 products providing detailed aerosol information and level 3 products offering aggregated statistics. The paper concludes that MODIS aerosol retrievals are accurate and useful for understanding aerosol radiative forcing and its impact on global climate.This work is a U.S. government work and is not protected by U.S. copyright law. It is published under the Public Domain Mark 1.0. The MODIS Aerosol Algorithm, Products, and Validation paper describes the development and evaluation of satellite algorithms for retrieving aerosol properties from NASA's Terra and Aqua satellites. The MODIS sensor provides daily global observations across a wide spectral range, enabling the derivation of aerosol optical thickness and size parameters over land and ocean. The paper details the aerosol products available, including optical thickness at multiple wavelengths, effective radius, and mass concentration. Validation against two years of AERONET data from 132 stations shows that MODIS optical thickness retrievals have uncertainties of ±0.03–0.05τ over ocean and ±0.05–0.15τ over land. The effective radius retrievals have an uncertainty of ±0.11 μm. The MODIS aerosol retrieval algorithm is described for both land and ocean, with the land algorithm using calibrated reflectances and cloud masks to identify and process aerosol data. The ocean algorithm includes cloud and sediment masking, and uses a lookup table to derive aerosol optical thickness, effective radius, and other parameters. The paper also discusses the validation of aerosol products, including comparisons with AERONET data, and highlights the accuracy and reliability of MODIS aerosol retrievals for climate studies. The MODIS aerosol products are available at various levels, with level 2 products providing detailed aerosol information and level 3 products offering aggregated statistics. The paper concludes that MODIS aerosol retrievals are accurate and useful for understanding aerosol radiative forcing and its impact on global climate.