Herein, the use of nanoemulsions (NEs) -described as metastable emulsions consisting of sub-500-nm sized droplets -in medicine is discussed. The ambiguity associated with defi ning NEs is elaborated upon, and the nature of NEs is contrasted with that of microemulsions (MEs). The various high-and low-energy methods, by which NE are prepared, are discussed, and stability issues are elaborated upon. Finally, specifi c examples concerning the use of NEs in medicine are given, including: drug delivery vehicles, mucosal vaccine vectors, topical antimicrobials and MRI/ ultrasonography contrast agents.