Electrolytes are fluids containing mobile charges. Much of the natural world is made up of electrolyte: the sea, animals and plants are all made up of largely of electrolyte.  In technology electrolytes are also important, with a key example being the finely-tuned electrolytes used in batteries and supercapacitors. Classical physical chemistry of electrolytes explains well the behavior of electrolytes at low ion-concentration, however a current challenge is to extend our knowledge to reach the high-concentration regime.  A particularly fascinating class of high-concentration electrolytes are the ionic liquids: salts which are liquid under ambient conditions despite containing no solvent.  Our experimental approach is to measure surface forces across ionic liquids and other concentrated electrolytes, allowing us to determine properties such as screening length, near-surface ordering, charge regulation and other bulk and surface properties of the electrolytes.