Ionic liquids (ILs) have emerged as a versatile class of compounds that offer unique physicochemical properties, transforming the field of sustainable chemistry. This chapter explores the role of ILs in nano-catalysis, highlighting their function as green solvents and stabilizing agents in catalytic reactions. Their applications in sustainable energy, such as fuel cells, batteries, and CO2 capture, underscore their potential to address global energy challenges. The development and use of biodegradable ionic liquids further enhance their environmental compatibility, paving the way for eco-friendly industrial applications. Finally, the chapter discusses emerging trends and future directions in IL research, including task-specific ILs, deep eutectic solvents, and hybrid systems, providing insights into the next frontier of green and sustainable chemistry.