Research into the properties and applications of ionic liquids (ILs) has accelerated over the last few decades, driven principally by the advanced reaction kinetics and specificity they offered for synthesis and catalysis. ILs display many highly desirable properties, including high electrical and thermal conductivities and wide electrochemical windows, all of which can be tuned by altering the nature of their constituent ions. The discovery that ILs mediate surfactant self-assembly increased interest further. X-ray and neutron scattering are powerful tools for elucidating structure in both simple and complex, mesostructured liquids that were soon applied to IL-based systems. Early work revealed that many IL solvents are themselves nanostructured, and comprise distinct polar and apolar domains produced by the solvophobic segregation of alkyl moieties. Over the last decade scattering techniques have been used to characterise the nanostructure of a diverse range of ILs. Recently, nanostructure changes in ILs produced by the dissolution of salts, polymers, small molecules and amphiphiles have begun to be elucidated. X-ray and neutron scattering have, and will continue to, play a fundamental role in understanding structure-property relationships in IL-based systems.