Deep eutectic liquids (DELs) - mixtures of high melting-point solids that form stable liquids near room temperature ¿ have recently emerged as a new class of novel solvents with many favourable properties. Our aim here is to understand the intermolecular interactions in such mixtures in order to optimise application-specific physical properties ranging from viscosity to thermal conductivity, solubility, catalysis and chemical reactivity for a variety of processes. Our goal is to develop DELs that mimic the properties of detergent solutions, microemulsions and other complex fluids that are widely used as formulations in industry and consumer products.