Phosphonium cation-based ionic liquids (ILs) are a readily available family of ILs that in some applications offer superior properties as compared to nitrogen cation-based ILs. Applications recently investigated include their use as extraction solvents, chemical synthesis solvents, electrolytes in batteries and super-capacitors, and in corrosion protection. At the same time the range of cation–anion combinations available commercially has also been increasing in recent years. Here, we provide an overview of the properties of these interesting materials and the applications in which they are appearing.