A workshop to bring together experts interested in combining multi-wavelength data from X-ray, infra-red, millimeter and radio surveys with optical data from LSST. We will discuss the challenges of combining key multi-wavelength datasets from surveys with UK leadership (e.g. XMM-Newton, VISTA, Euclid, Herschel, LOFAR, SKA) with the LSST data. We will put together a plan for bench-marking and testing existing algorithms as well as developing new methodology for data-fusion that will be relevant in the LSST era.