The second release of the XMM OM Serendipitous Source Survey Catalogue (XMM-SUSS2) was produced by processing the XMM-Newton Optical Monitor (OM) data obtained from the beginning of the mission (2000) until the end of 2012. The latest release, XMM-SUSS2.1, now includes an extra year of data to the end of 2013. The data processing was performed at the European Space Astronomy Centre (ESAC, Spain) and at Mullard Space Science Laboratory (MSSL UCL, U.K.) by using the XMM Science Analysis Software system (SAS) version 14.0. In addition to covering a larger observation period, this release differs from the first release (XMM-SUSS) by inclusion of all the OM observations (not only those containing UV filters) and by performing source detection on stacked images, thus facilitating the detection of fainter sources. The number of observations (OBSIDs) included in the catalogue is 7,170. The total number of entries included in the catalogue is 6,246,432. They correspond to 4,329,363 sources, of which 831,582 have multiple entries in the source table, corresponding to different observations.