Composites based on Metal-Organic Frameworks (MOFs) are an emerging class of porous materials that have been shown to possess unique functional properties. Nanoparticles at MOFs composites combine the tailorable porosity of MOFs with the versatile functionality of metal or metaloxide nanoparticles. A wide range of nanoparticles at MOFs have been synthesised and their performance characteristics assessed in molecular adsorption and separation, catalysis, sensing, optics, sequestration of pollutants, drug delivery, and renewable energy. This review covers the main research areas where nanoparticles at MOFs have been strategically applied and highlights the scientific challenges to be considered for their continuing development. ; P.F. and C.J.D. gratefully acknowledges the Australian Research Council for funding DECRA DE120102451 and Future Fellowships FT100100400, respectively. D.M., I.I. and A.Y. thank the EC FP7 ERC-Co 61594.l ; Peer Reviewed