The XMM-Newton Science Archive (XSA) became publicly available in April 2002. The XSA content is regularly updated with all the generated ODF, SDF and PPS products and with updated versions of the catalogues of EPIC sources, OM sources and Slew Survey sources, and ancillary info like associated proposal abstract, publications, etc.
In 2019 the XMM-Newton SOC performed the third bulk reprocessing of all XMM-Newton data obtained since the beginning of the mission in 1999, and all data are thus processed with SAS 18.0 or higher.
PIs of XMM-Newton observations can retrieve their own proprietary data using their password-protected XSA account.
Public data can be retrieved through the XSA user web interface: https://nxsa.esac.esa.int/nxsa-web/. Data can also be retrieved directly from the archive via URL or command line (see examples at the Command & URL access help page: https://nxsa.esac.esa.int/nxsa-web/#aio). XSA database tables can be queried using ADQL (Astronomical Data Query Language), see the Table Access Protocol (TAP) help page (https://nxsa.esac.esa.int/nxsa-web/#tap) for details.
Public and propietary XMM-Newton data can also be downloaded through the Python module astroquery.esa.xmm_newton (see https://nxsa.esac.esa.int/nxsa-web/#astroquery for details).
http://www2.le.ac.uk/departments/physics-and-astronomy/research/src/Missions/xmm-newton/instrument
EPIC/pn at the Max-Planck-Institut für extraterrestrische Physik
http://www.mpe.mpg.de/33319/XMM-Newton
RGS at the Space Research Organization Netherlands
http://www.sron.nl/missions-xmm-newton
OM at the Mullard Space Science Laboratory
http://www.mssl.ucl.ac.uk/www_astro/xmm/om/om.html
SSC: Survey Science Centre
http://xmmssc.irap.omp.eu/
NASA's XMM-Newton Guest Observer Facility
http://heasarc.gsfc.nasa.gov/docs/xmm/xmmgof.html
PIMMS (HEASARC)
http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html
XSPEC (HEASARC)
http://heasarc.gsfc.nasa.gov/docs/xanadu/xspec/
Additional information on XMM-Newton can always be obtained from other locations under the SOC home page, at http://www.cosmos.esa.int/web/xmm-newton/.