Drug delivery systems are designed in order to achieve maximum therapeutic efficacy of the drugs while reducing their toxicity. The modern drug dosage forms have been the result of a long scientific research in the field. Using sophisticated technologies and exploring novel excipients with outstanding physicochemical characteristics have led to the development of modern novel drug delivery systems from simple pills and mixtures. Emulsions are biphasic systems having one phase dispersed in the other phase in the form of droplets ranging in diameter from 0.1 to 100 ?m. Thermodynamically, they are unstable in nature, but can be made stable with the applications of emulsifiers or emulgents. , the surfactants used as emulsifiers are termed as interphaseor intermediate The “Nanoemulsion” term is used for thermodynamically stable isotropically clear dispersion of two immiscible liquids like water and oil stabilized through the surfactant molecules interfacial film. They are novel drug delivery systems in which oil is emulsified in an aqueous system in the form of droplets with a mean diameter 100-500 nm. Nanoemulsions have found wide spread applications as drug delivery vehicles due to some of their distinguished characteristics. There is a growing interest for using of Nano/sub-micron particles in the technology of pharmaceutical, cosmetic and also food industries. Nanoemulsions are also preferred due to their administration through multiple routes. They are used for efficient drug delivery through skin because of the large surface area they provide for the drug penetration. Moreover, they have been nontoxic and nonirritant to the mucous membrane and skin tissues. Their fluidity and avoidance of thickeners in theirformulations make them transparentwithaestheticphysicalappearance. In this paper, a comprehensive review is presented to give basic ideas about properties of Nano emulsions, their preparation methods, and evaluations.