Since the introduction of ionic liquids (IL) in 1914, there has been a growing interest in this class of materials, because of their unique properties. Ionic liquids are organic salts, melting below 100 degrees C, and are generally non-volatile and nonflammable. By combination of different anions and cations, a large number of ionic liquids can be synthesized. The extraordinary characteristics of ILs and the possibility of synthesizing large number of ILs make them as an appropriate medium for various chemical processes and applications. In this review, first, we give a brief overview on IL important physical properties, and then we look into different IL applications, considering recent studies and findings and the future prospects of using IL in each application. This review gives a reader a complete knowledge about various ILs application all together. In addition, it reveals the areas of application which will grow in future and can gain industrial importance. ILs applications in separation processes, lignocelluloses pretreatment, enhanced oil recovery (EOR), biocatalytic reactions, lubrication and electrochemistry are discussed. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.