In this review, the formation, characterization, properties and applications of nano-emulsions are reviewed and summarized. Nanoemulsions are submicron sized emulsions that are under extensive investigation as drug carriers for improving the delivery of therapeutic agents. Nanoemulsions are the thermodynamically stable isotropic system in which two immiscible liquid (water and oil) are mixed to form a single phase by means of an appropriate surfactants. Due to their small droplet size nano-emulsions possess stability against sedimentation or creaming with Ostwald ripening forming the main mechanism of nanoemulsion breakdown. Nanoemulsion droplet sizes fall typically in the range of 20-200nm. Diameter and surface properties of droplets of nanoemulsion plays an important role in the biological behavior of the formulation. Nanoemulsion show great promise for the future of cosmetics, diagnostics, drug therapies, and biotechnologies. The main application of nanoemulsions is the preparation of nanoparticles using a polymerizable monomer as the disperse phase (the so-called miniemulsion polymerization method) where nanoemulsion droplets act as nanoreactors. Another interesting application which is experiencing an active development is the use of nanoemulsions as formulations, namely for controlled drug delivery and targeting.