Ionic liquids can simultaneously assume multiple solvent roles, because they are strongly polar and polarizable solvents and binary solutions and frequently contain very hydrophobic components. When the cation and anion functional groups are tuned appropriately, ionic liquids can be used as designer solvents for a broad range of applications. In this Account, we discuss our spectroscopic studies on the intermolecular interactions, dynamics, solvation, transport, and friction in ionic liquids, as compared with information obtained from macroscopic experiments including viscometry and calorimetry.