The XMM-Newton Observatory, a cornerstone mission of the European Space Agency's Horizon 2000 program, is the largest scientific satellite launched by ESA to date. This paper provides an overview of the observatory's key characteristics and operations. The three mirror modules, each consisting of 58 Wolter I mirrors, offer a large effective area for X-ray spectroscopy of faint sources. The in-orbit performance and preliminary calibrations of the observatory are discussed, highlighting the successful calibration of the telescopes' point responses and effective areas. The spacecraft, weighing 4 tons and 10 meters long, includes two large payload modules connected by a carbon fiber tube. The Service Module houses most of the sub-systems and instruments, including the Optical Monitor, star trackers, and the three X-ray Mirror Modules. The orbit, with a period of about 48 hours, allows for cooling of the instruments to cryogenic temperatures. The ground segment, consisting of two primary ground stations (Perth and Kourou), ensures continuous data transmission and processing. The Observation Data Files (ODFs) are provided to the Guest Observer community, along with calibration files (CCFs) for data processing. The Science Analysis Sub-System (SAS) software supports interactive data analysis, and calibration verification is ongoing. The paper also outlines the data flow from the spacecraft to the ground segment and the final delivery of calibrated data to the scientific community.The XMM-Newton Observatory, a cornerstone mission of the European Space Agency's Horizon 2000 program, is the largest scientific satellite launched by ESA to date. This paper provides an overview of the observatory's key characteristics and operations. The three mirror modules, each consisting of 58 Wolter I mirrors, offer a large effective area for X-ray spectroscopy of faint sources. The in-orbit performance and preliminary calibrations of the observatory are discussed, highlighting the successful calibration of the telescopes' point responses and effective areas. The spacecraft, weighing 4 tons and 10 meters long, includes two large payload modules connected by a carbon fiber tube. The Service Module houses most of the sub-systems and instruments, including the Optical Monitor, star trackers, and the three X-ray Mirror Modules. The orbit, with a period of about 48 hours, allows for cooling of the instruments to cryogenic temperatures. The ground segment, consisting of two primary ground stations (Perth and Kourou), ensures continuous data transmission and processing. The Observation Data Files (ODFs) are provided to the Guest Observer community, along with calibration files (CCFs) for data processing. The Science Analysis Sub-System (SAS) software supports interactive data analysis, and calibration verification is ongoing. The paper also outlines the data flow from the spacecraft to the ground segment and the final delivery of calibrated data to the scientific community.