The XMM-Newton observatory is a cornerstone mission of the European Space Agency (ESA) Horizon 2000 program. This spacecraft, the largest ever flown by ESA for a scientific program, was launched on December 10, 1999, carrying a payload funded by ESA member states and the USA (NASA). The scientific payload comprises three CCD imaging cameras (European Photon Imaging Cameras, EPIC), sensitive in the 0.1-15 keV band, and two Reflecting Grating Spectrometers (RGS), sensitive in the 0.3-2.1 keV band, and characterized by a resolving power E/{Delta}E = 100 to 800. The X-ray instruments are complemented by an Optical Monitor, sensitive in the 150-650nm band, which allows simultaneous multiwavelength monitoring of celestial sources. The XMM-Newton observational program is determined on the bases of the proposals sent in response to Announcement of Opportunities, and selected by peer review panels. The XMM-Newton Science Archive (XSA) contains all the science data of all the performed observations. Its user interface (http:xmm.vilspa.esa.es/xsa) allows a user to retrieve them after the 1-year proprietary period has expired. Calibration observations are normally not covered by proprietary rights; their data being therefore public. Target of Opportunity and Discretionary Time observations have a 6-months proprietary period. For each archived observation, the XSA stores Observation Data Files (ODF) and Pipeline Processing System (PPS) products, if available, as well as the XMM-Newton EPIC serendipitous catalogue, the OM source catalogue and the Slew Survey Source Catalogue (see the catalogues documentation at http://xmm.esac.esa.int/xsa). The ODF comprises raw telemetry files, reformatted in FITS format, and contains uncalibrated information. The PPS products are a collection of top-level, validated scientific and cross-correlation products, routinely generated by the Science Survey Center, University of Leicester, UK (http://xmmssc-www.star.le.ac.uk). The content of the XSA is updated daily. The latest version of all the scientific data is made available through its interface. Systematic reprocessing of all the XMM-Newton telemetry is periodically carried on during the mission. The last bulk reprocessing was performed in 2007. The XMM-Newton observation log lists all the science observations included in the XSA. This log gives observation details and provides links to quick-look scientific products, to documents describing XMM-Newton science and calibration data, and to the SAS (Science Analysis System), a specific software package designed to reduce and analyze XMM-Newton data. Additional links in the log allows a user to start a retrieval session for the data of an observation, whenever not protected by proprietary rights. XMM-Newton HelpDesk: http://xmm.esac.esa.int/external/xmm_user_support/helpdesk.shtml
