Transdermal drug delivery, in which drugs are administered through the skin, has been attracting much attention because it can bypass the first–pass effect in the liver, maintain the effective drug concentration in blood, avoid the pain and the risks of accidents in injection. Since the skin plays an important role as a barrier preventing the entry of foreign substances from the outside, a special technique is required to achieve the effective transdermal delivery of drugs. In this review, we introduce the latest transdermal drug delivery systems using emulsions. The use of emulsions enables to deliver high–molecular–weight drugs, which are usually difficult to permeate through the skin. Emulsions combined with a skin enhancer or ionic liquids are found to be useful for the effective transdermal delivery of biomolecules such as peptides or proteins.