ILs are identified as innovative designer solvents and advanced materials that can be utilized in a wide range of cutting-edge green processes and industrial applications. Ionic fluids inherently carry a higher degree of complexity than systems comprised of neutral species. They exhibit an exceptional combination of properties that originate primarily from their dual organic and ionic nature. A fundamental understanding of the diverse interactions and the microscopic mechanisms that give rise to the non-trivial spatial and dynamical behavior in this category of ionic fluids is required. Molecular simulation methods are  developed and implemented for the study of their complex microscopic behavior and the prediction of a wide range of properties (thermodynamic, dynamic, transport, sorption,permeability, selectivity) of pure systems and their mixtures with gases.