In this Perspective, we provide a detailed discussion of the techniques and methods used for determining the solubility of gases in ionic liquids (ILs). This includes various experimental measurement techniques, equation of state (EOS) modeling, and predictive molecular-based modeling. Many of the key papers from the past 15 years are discussed and put into the context of the latest advances in the field. Limitations of these methods plus future developments and new research opportunities are discussed. (C) 2017 American Institute of Chemical Engineers.