Ionic liquids (ILs) are revolutionary materials composed entirely of ions and remaining liquid below 100 °C, often under ambient conditions. Their unique properties, including negligible vapor pressure, high thermal stability, and tunable structural characteristics, make them highly versatile. This review provides a comprehensive analysis of ILs by systematically exploring their physicochemical properties, such as density, viscosity, thermal stability, and phase behavior under various conditions. The impact of water on IL behavior, IL–IL mixtures, and structure–property relationships is critically examined. Technological applications, particularly in gas capture, energy storage, and drug delivery, are evaluated, alongside a techno-economic analysis discussing market dynamics, commercialization barriers, and lifecycle considerations. Environmental sustainability, biodegradability, and regulatory aspects are also assessed. By bridging fundamental understanding with application-driven insights, this review identifies pathways for advancing ILs as sustainable enablers of clean technologies.
