The paper provides an overview of the SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) mission and its scientific objectives. SCIAMACHY is designed to measure sunlight transmitted, reflected, and scattered by the Earth's atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) with moderate spectral resolution (0.2–1.5 nm). The instrument will measure earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere in occultation. The extraterrestrial solar irradiance and lunar radiance will also be determined from observations of the sun and moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the Earth's surface are determined by comparing earthshine radiance and solar irradiance. Inversion of these ratios provides information on the distribution of atmospheric constituents and the spectral reflectance of the Earth's surface. The main scientific objectives of the SCIAMACHY mission include improving our understanding of global atmospheric changes, tropospheric pollution, stratosphere-troposphere exchange processes, stratospheric ozone chemistry, and the impact of natural phenomena such as volcanic eruptions and solar variability. The instrument will measure the backscattered sunlight that reaches the Earth's surface, allowing for the retrieval of tropospheric columns of various trace gases and aerosols. The combined use of nadir and limb measurements will enable the determination of tropospheric column amounts down to the ground or cloud top, depending on cloud cover. The SCIAMACHY instrument is a passive remote sensing moderate-resolution imaging spectrometer, comprising a mirror system, a telescope, a spectrometer, and thermal and electronic subsystems. It measures in the wavelength range from 240 nm to 2380 nm, with a spectral resolution of 0.24 to 1.48 nm. The instrument is designed to have high spectral stability and radiometric accuracy, with dedicated calibration measurements to ensure data quality. The instrument operates in three viewing geometries: nadir, limb, and solar/lunar occultation, providing global coverage at the equator after 6 days. The retrieval methods used by SCIAMACHY include Differential Optical Absorption Spectroscopy (DOAS) and the Full Retrieval Method (FURM). DOAS is used to detect atmospheric constituents by fitting the measured earthshine radiance and solar irradiance to a model that accounts for absorption and scattering processes. FURM, based on optimal estimation, matches the calculated radiance to the measured radiance by iteratively modifying atmospheric parameters. The precision of SCIAMACHY measurements is estimated to be high, with noise and instrument performance evaluated using various sensitivity studies.The paper provides an overview of the SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) mission and its scientific objectives. SCIAMACHY is designed to measure sunlight transmitted, reflected, and scattered by the Earth's atmosphere or surface in the ultraviolet, visible, and near-infrared wavelength region (240–2380 nm) with moderate spectral resolution (0.2–1.5 nm). The instrument will measure earthshine radiance in limb and nadir viewing geometries and solar or lunar light transmitted through the atmosphere in occultation. The extraterrestrial solar irradiance and lunar radiance will also be determined from observations of the sun and moon above the atmosphere. The absorption, reflection, and scattering behavior of the atmosphere and the Earth's surface are determined by comparing earthshine radiance and solar irradiance. Inversion of these ratios provides information on the distribution of atmospheric constituents and the spectral reflectance of the Earth's surface. The main scientific objectives of the SCIAMACHY mission include improving our understanding of global atmospheric changes, tropospheric pollution, stratosphere-troposphere exchange processes, stratospheric ozone chemistry, and the impact of natural phenomena such as volcanic eruptions and solar variability. The instrument will measure the backscattered sunlight that reaches the Earth's surface, allowing for the retrieval of tropospheric columns of various trace gases and aerosols. The combined use of nadir and limb measurements will enable the determination of tropospheric column amounts down to the ground or cloud top, depending on cloud cover. The SCIAMACHY instrument is a passive remote sensing moderate-resolution imaging spectrometer, comprising a mirror system, a telescope, a spectrometer, and thermal and electronic subsystems. It measures in the wavelength range from 240 nm to 2380 nm, with a spectral resolution of 0.24 to 1.48 nm. The instrument is designed to have high spectral stability and radiometric accuracy, with dedicated calibration measurements to ensure data quality. The instrument operates in three viewing geometries: nadir, limb, and solar/lunar occultation, providing global coverage at the equator after 6 days. The retrieval methods used by SCIAMACHY include Differential Optical Absorption Spectroscopy (DOAS) and the Full Retrieval Method (FURM). DOAS is used to detect atmospheric constituents by fitting the measured earthshine radiance and solar irradiance to a model that accounts for absorption and scattering processes. FURM, based on optimal estimation, matches the calculated radiance to the measured radiance by iteratively modifying atmospheric parameters. The precision of SCIAMACHY measurements is estimated to be high, with noise and instrument performance evaluated using various sensitivity studies.