Tremendous strides have been made in the prediction of thermodynamic and transport properties from molecular simulations and theoretical models. Nonetheless, experimentation plays a critical role in both the conception of new chemical processes and their development and design. This is especially true when developing or exploring unconventional materials. We will give a number of examples of the importance of experimentation from our work with ionic liquids, which are organic salts with low melting points. We will show how serendipitous experiments led to the development of ionic liquids for gas separations and the use of carbon dioxide to separate mixtures of ionic liquids and organics. In addition, we will show how experimental results have been key to evaluating thermodynamic models of phase behavior involving ionic liquids.