Ionic liquids (ILs) are typically characterized as ionic compounds that possess a melting point less than 100 °C. The first IL was ethyl ammonium nitrate which was identified in 1914 by Paul Walden. These substances are recognized for their remarkable performance as chemicals. They exhibit extremely low vapor pressures and can be tailored for specific interactions with various chemicals and materials, including catalysts, solutes, and interfaces involving liquids and gases. ILs demonstrate exceptional thermal and electrochemical stability, and their nucleophilic properties can be finely adjusted. Composed entirely of ions, ILs are increasingly being used as environmentally friendly solvents in numerous organic synthesis processes because their high solvent power and minimal volatility make them a sustainable alternative to traditional volatile molecular solvents in various organic reactions as solvents, catalysts, reagents, or combinations. ILs promote eco-friendliness, sustainability, and principles of the circular economy. Since the ILs line up with the accordance of green chemistry principles, ongoing research into eco-friendly, biodegradable ILs is crucial for their full incorporation into the framework of a circular economy. Their relationship with the circular economy is reinforced through multiple pathways that promote sustainability, improve resource efficiency, and reduce waste. This chapter delivers an inclusive analysis about the necessity and function of ILs in the organic reactions along with a critical discussion on the extent to which ILs can replace conventional solvents.