Ionic liquids (ILs) are an exciting class of compounds with unique properties that make them attractive for industrial applications. Among their valuable features, an immesurably low vapor pressure and a liquid state at or near ambient conditions are found at the top of the list. In this book, thermophysical and transport properties of ionic liquids are theoretically investigated by means of molecular simulation techniques. Quantum calculations are used as a supportive tool to force field development work. This research task is guided and supported by experimental studies. Studied cations include imidazolium-, pyridinium- and triazolium-based structures with different inorganic anions such as hexafluorophosphate, bis(trifluoromethanesulfonyl)imide, nitrate and perchlorate. Static properties computed include gravimetric densities, volumetric expansivities, isothermal compressibilities, heat capacities, cohesive energy densities as well as the liquid structure. Analysis of the dynamic properties of ionic liquid systems is also carried out yielding information on the rotational dynamics and transport properties.