The primary objectives of the Chandrayaan-1 mission are simultaneous chemical, mineralogical and topographic mapping of the lunar surface at high spatial resolution. These data should enable us to understand compositional variation of major elements, which in turn, should lead to a better understanding of the stratigraphic relationships between various litho units occurring on the lunar surface. The major element distribution will be determined using an X-ray fluorescence spectrometer (LEX), sensitive in the energy range of 1-10 keV where Mg, Al, Si, Ca and Fe give their Kα lines. A solar X-ray monitor (SXM) to measure the energy spectrum of solar X-rays, which are responsible for the fluorescent X-rays, is included. Radioactive elements like Th will be measured by its 238.6 keV line using a low energy gamma-ray spectrometer (HEX) operating in the 20-250 keV region. The mineral composition will be determined by a hyper-spectral imaging spectrometer (HySI) sensitive in the 400-920 nm range. The wavelength range is further extended to 2600 nm where some spectral features of the abundant lunar minerals and water occur, by using a near-infrared spectrometer (SIR-2), similar to that used on the Smart-1 mission, in collaboration with ESA. A terrain mapping camera (TMC) in the panchromatic band will provide a three-dimensional map of the lunar surface with a spatial resolution of about 5 m. Aided by a laser altimeter (LLRI) to determine the altitude of the lunar craft, to correct for spatial coverage by various instruments, TMC should enable us to prepare an elevation map with an accuracy of about 10 m. Four additional instruments under international collaboration are being considered. These are: a Miniature Imaging Radar Instrument (mini-SAR), Sub Atomic Reflecting Analyser (SARA), the Moon Mineral Mapper (M3) and a Radiation Monitor (RADOM). Apart from these scientific payloads, certain technology experiments have been proposed, which may include an impactor which will be released to land on the Moon during the mission. Salient features of the mission are described here. The ensemble of instruments onboard Chandrayaan-1 should enable us to accomplish the science goals defined for this mission.