Ionic liquids are molten salts which exist as a group of non-molecular compounds having an ionic structure. The synthesis of ionic liquids involves the formation of the desired cation and anion exchange. Ionic liquids can be categorized under five basic classes that include ammonium, phosphonium, imidazolium, pyridinium, and pyrrolidinium. Characteristic features of ionic liquids are low vapor pressure at room temperature as well as high thermal stability for a wide range of temperatures. The physical and chemical properties such as thermal stability, viscosity, and solubility in water can be varied by just altering the combination of cations and anions. A solvent is any liquid that can dissolve another substance. Ionic liquids are used as solvents in different areas of chemistry such as organic synthesis, electrochemistry, extraction, spectroscopy and mass spectrometry. They are also applied in separation techniques such as liquid and gas chromatography or capillary electrophoresis. This book includes researches related to the synthesis, characterization and applications of solvents and ionic liquids. It includes contributions of experts and scientists which will provide innovative insights into this area of study.