Sustainability in chemistry is strongly connected to the green chemistry and circular economy concepts, having as objectives the reduction of the usage of hazardous substances and of energy consumption, the minimization of the resource input and wastes and the minimization of the emissions and energy leakage. On this basis, a sustainable chemistry must ensure the longevity of humans, animals and ecosystems by allowing for serene development, and also maintaining economic competitiveness to create profit and business. In this multidisciplinary approach, the role of the solvent is very important. Many organic solvents are harmful, toxic and environmentally damaging, and their use poses risks to both human health and the environment. Therefore, to avoid any negative effects, in addition to eliminating solvents exhibiting such negative properties, a proper solvent should: (1) act simultaneously as solvent and reagent; (2) control the quality of the products; (3) reduce the number of synthetic steps; (4) avoid the formation of by-products; (5) improve product separation; and (6) be able to be recycled. In this context, ionic liquids (ILs) emerged as promising green solvents for environmentally friendly synthesis. Although their production is not always green, these structures demonstrate efficiency in several ways, such as process intensification through catalysis, sustainable catalytic biocatalytic processes for biomass valorization, CO2 valorization and sustainable reactions in organic and pharmaceutical chemistry. In addition, there are examples in which ILs functionalized on various supports demonstrated enhanced catalytic efficiency. All of these offer new perspectives in the utilization of these compounds.