Deep eutectic solvents (DESs) constitute a unique class of liquid systems possessing immense potential as less hazardous alternatives to conventional organic solvents for a variety of applications in chemical industries. DESs are multicomponent mixtures in molten phase of solid compounds mixed at particular compositions where the liquid phase is accessed through heating at higher temperatures, followed by normal cooling to room temperature or near room temperature. By definition, the liquid phase temperature must be significantly lower than the individual melting temperatures of the mixture components and as a result, is distinctly different from the prediction based on depression of freezing point via colligative effects. Often, the term DESs is used somewhat loosely to encompass the molten phase of the multicomponent mixtures at temperatures and compositions that are away from those corresponding to the eutectic points. Several outstanding solvent features, such as, viscosity and polarity turnabilities, relatively lesser environmental footprints, easy to prepare and handle, low vapor pressure, wider thermal and electrochemical windows, etc. have made DESs as popular solvents as reaction media not only for targeted chemical synthesis but also for engineering materials related to technological applications. Naturally therefore, DESs are finding applications in extraction of natural compounds , gas absorption , synthesis of targeted biopolymers and organic compounds. Recently, ionic DESs have been emerged as potential non-flammable electrolytes for lithium-ion batteries. Ionic deep eutectic solvents act as a bridge between ionic liquids (ILs) and electrolyte solutions. Ionic DESs are comprised of hydrogen bond donors (HBD) and ions generated from the dissociation of the added electrolytes. Substantial charge delocalization induced by the extensive interspecies (ion-amide) H-bond interactions causing frustrations in the ionic lattices provides the enthalpic support for formation of DESs. The entropy gains for being in the liquid phase then completes the driving force behind the stable liquidous regime in DESs, although theoretical/computational investigation for the composition and temperature dependent entropy gain (both rotational and translational) are still unavailable. Different experiments, such as, time-resolved fluorescence experiments, dielectric relaxation and conductivity measurements, and femtosecond Raman induced Kerr effect spectroscopic (fs-RIKES) measurements have been carried out in the last several years and each of these measurements indicated micro heterogeneous relaxation dynamics for the studied ionic DESs.