Microemulsions offer an innovative approach applicable to pharmaceutical compounding for increasing solubility, permeability, and bioavailability of some drug substances. They can also enhance stability, both chemical and physical, and be prepared as either oil in water or water in oil systems. Microemulsions are thermodynamically stable, optically transparent, isotropic mixtures of oil, water surfactant, and a cosurfactant. The type of emulsion formed depends upon the properties of the oil and surfactants. The commercial manufacture and the compounding of microemulsions have become a part of the design and development of new drug delivery systems.