Knowledge of the physicochemical properties of ionic liquids is important for designing ionic liquid based separation and reaction processes as well as for electrochemical applications. In this presentation, we report results from experimental measurements of a number of different properties of a collection of ionic liquids. The solubility and diffusivity of carbon dioxide and ammonia were measured using a novel pressure transient method. The conductivity of the ionic liquids was measured using a custom built electrochemical cell. The electrochemical window of the ionic liquids has been estimated using cyclic voltametry. Differential scanning calorimetry was used to determine the specific heat of ionic liquids. Viscosity and density measurements have also been performed with clean ionic liquids and with ionic liquids saturated with water as well as other solutes. Results from these measurements and relationships between physicochemical characteristics and ionic liquid structure will be discussed.