Ionic liquids are excellent substitutes for traditional organic solvents in many typical organic reactions, often producing higher selectivities as well as higher yields, and enhancing the reaction rate. Additionally, they can serve as catalyst immobilization for the easy recycling of homogeneous catalysts without need for special functionalization, and have been successfully employed as electrolytes in electrochemistry. "Tailor-made" solvents (optimization of the ionic liquid's characteristics) can be achieved through a broad choice of anion and cation combinations.

Ionic liquids are attractive solvents as they are non-volatile, non-flammable, have a high thermal stability and are relatively inexpensive to manufacture. They usually exist as liquids well below room temperature up to a temperature as high as 200oC.

The key point about ionic liquids is that they are liquid salts, which means they consist of a salt that exists in the liquid phase. They are not simply salts dissolved in liquid. Usually one or both of the ions is particularly large and the cation has a low degree of symmetry, these factors result in ionic liquids having a reduced lattice energy and hence lower melting points.Many ionic liquids have even been developed for specific synthetic problems. For this reason, ionic liquids have been termed "designer solvents".