Ionic liquids (ILs) are ion-based materials that remain liquid below 100 °C, offering unique properties like low vapor pressure, thermal stability, and tunable chemistry. This review explores their structure–property relationships, behavior in various environments, and practical uses in gas capture, energy storage, and drug delivery. It also highlights market challenges, sustainability, and future directions for ILs as enablers of clean technologies. The extensive review article is published in ACS Energy & Fuels and selected for cover art of the issue.
