The SSC is responsible, on behalf of ESA, for the construction of the XMM-Newton Serendipitous Source Catalogues. To date, there have been four releases of the (EPIC) X-ray catalogue: 1XMM, in April 2003, 2XMMp in July 2006, 2XMM in 2007 (2XMMp was an interim version of the more complete and extensive 2XMM catalogue) and an incremental catalogue, 2XMMi, in August 2008. Creation of the catalogues involves the selection of suitable datasets, (possibly) a bulk reprocessing of all the data, compiling the catalogue from the source lists of the individual observations, screening and verifying the associated data products, and making the catalogues available to the scientific community in close collaboration with ESA. A number of added-value products, such as image thumbnails and web-pages for each source are also generated separately. Each catalogue release uses as many of the publicly available datasets as possible, though some observations are excluded for various reasons, e.g. very low exposure, or cases with processing or pathological problems.