The XMM-Newton observatory is a major mission of the European Space Agency's Horizon 2000 program, the largest scientific satellite launched by ESA. This paper summarizes the key characteristics of the observatory relevant to scientific operations. The observatory's three mirror modules, with an unprecedentedly large effective area, enable high-quality X-ray spectroscopy of faint sources. The in-orbit performance and preliminary calibrations of the observatory are briefly described. Observations from the calibration and performance verification phase, which are public, are listed. The data flow from the spacecraft to the ground segment and the production of preliminary science products for users is also discussed. XMM-Newton was launched on December 10, 1999, into a 48-hour orbit. It is the largest scientific satellite ever launched by ESA. The spacecraft consists of two large payload modules connected by a long carbon fiber tube, forming the telescope optical bench. The focal plane assembly includes the two Reflection Grating Spectrometers, an EPIC PN detector, and two EPIC MOS imaging detectors. The spacecraft service module contains most of the spacecraft subsystems, including the Optical Monitor, star trackers, and the three X-ray mirror modules. Each of the three X-ray telescopes consists of 58 Wolter I mirrors, providing a large collecting area over a wide energy band. The mirrors are replicated from superpolished gold-coated mandrels using a nickel electroforming technique. The point spread functions and effective areas of the telescopes were characterized on-ground and validated in-orbit. The telescopes' point responses measured in-orbit are identical to on-ground calibration measurements, with a spatial resolution of ~5 arcsec. The telescopes have a high stray-light rejection efficiency, as verified by observations of the Crab nebula. The spacecraft is equipped with redundant star trackers, providing an absolute measurement accuracy of 4 arcsec. The spacecraft's orbit is highly eccentric, with a 48-hour period, allowing the five main X-ray cameras to be cooled to -80°C to -100°C using passive radiators. The orbit is chosen to avoid the radiation belts, limiting operations to altitudes ≥60,000 km. The spacecraft's attitude is monitored and corrected for any deviations, ensuring stable operations. The data flow from the spacecraft to the ground segment involves multiplexing science data with housekeeping data and telemetry, transmitted at 64 kbit/s. The data are processed into Observation Data Files (ODFs) for transmission to the science community. The Current Calibration File (CCF) is also provided to ensure accurate calibration. The ODFs are processed by the Survey Science Centre to produce standard products, including calibrated event lists, source detection lists, and standard image, spectral, and timing products. These products are used for interactive analysis by the Guest Observer community. The Science Analysis Sub-System (SAS) is usedThe XMM-Newton observatory is a major mission of the European Space Agency's Horizon 2000 program, the largest scientific satellite launched by ESA. This paper summarizes the key characteristics of the observatory relevant to scientific operations. The observatory's three mirror modules, with an unprecedentedly large effective area, enable high-quality X-ray spectroscopy of faint sources. The in-orbit performance and preliminary calibrations of the observatory are briefly described. Observations from the calibration and performance verification phase, which are public, are listed. The data flow from the spacecraft to the ground segment and the production of preliminary science products for users is also discussed. XMM-Newton was launched on December 10, 1999, into a 48-hour orbit. It is the largest scientific satellite ever launched by ESA. The spacecraft consists of two large payload modules connected by a long carbon fiber tube, forming the telescope optical bench. The focal plane assembly includes the two Reflection Grating Spectrometers, an EPIC PN detector, and two EPIC MOS imaging detectors. The spacecraft service module contains most of the spacecraft subsystems, including the Optical Monitor, star trackers, and the three X-ray mirror modules. Each of the three X-ray telescopes consists of 58 Wolter I mirrors, providing a large collecting area over a wide energy band. The mirrors are replicated from superpolished gold-coated mandrels using a nickel electroforming technique. The point spread functions and effective areas of the telescopes were characterized on-ground and validated in-orbit. The telescopes' point responses measured in-orbit are identical to on-ground calibration measurements, with a spatial resolution of ~5 arcsec. The telescopes have a high stray-light rejection efficiency, as verified by observations of the Crab nebula. The spacecraft is equipped with redundant star trackers, providing an absolute measurement accuracy of 4 arcsec. The spacecraft's orbit is highly eccentric, with a 48-hour period, allowing the five main X-ray cameras to be cooled to -80°C to -100°C using passive radiators. The orbit is chosen to avoid the radiation belts, limiting operations to altitudes ≥60,000 km. The spacecraft's attitude is monitored and corrected for any deviations, ensuring stable operations. The data flow from the spacecraft to the ground segment involves multiplexing science data with housekeeping data and telemetry, transmitted at 64 kbit/s. The data are processed into Observation Data Files (ODFs) for transmission to the science community. The Current Calibration File (CCF) is also provided to ensure accurate calibration. The ODFs are processed by the Survey Science Centre to produce standard products, including calibrated event lists, source detection lists, and standard image, spectral, and timing products. These products are used for interactive analysis by the Guest Observer community. The Science Analysis Sub-System (SAS) is used