An au pair (/oʊˈpɛər/; pl.: au pairs) is a person working for, and living as part of, a host family. Typically, au pairs take on a share of the family’s responsibility for child care as well as some housework, and receive a monetary allowance or stipend for personal use. Au pair arrangements are often subject to government restrictions which specify an age range usually from mid teens to late twenties, and may explicitly limit the arrangement to females. The au pair program is considered a form of cultural exchange that gives the family and the au pairs a chance to experience and learn new cultures.

Arrangements differ between Europe, where the concept originated, and North America. In Europe, au pairs are only supposed to work part-time, and they often also study part-time, generally focusing on the language of the host country. In the United States, they may provide full-time childcare. In 1969, the European Agreement on Au Pair Placement was signed, and it came into force in 1971. Au pair companies in the United States have significant non-refundable fees once the au pair arrives in the country. The contract does not guarantee childcare, despite many families' reliance on the program.

Unlike many other types of domestic assistants, the au pair is considered a part of the host family and not merely an employee. In some countries the au pair wears a uniform, but more commonly the au pair only follows the host family's dress code and wears attire appropriate for the work description, typically including a protective apron.