Microemulsion (ME) has been attracted much interest among researchers in various fields. This is also the case among pharmaceutical scientists, and this technique has already been employed for a marketed product for oral administration. The use of ME for other administration routes, such as transdermal, ocular, and intravenous delivery, has also been under development. These ME formulations offer various advantages such as enhanced bioavailability of drugs and ease of production. The cancellation of intra-individual deviations in absorption behavior has also been investigated for oral ME formulations. This review will summarize and discuss recent progress in ME formulations.