An au pair is a single and childless young adult aged between 18 and 30 years, who travels to a foreign country for a given period to live there within a host family. The au pair is to be considered as a full member of the family during the whole stay. As such, he or she helps the family with taking care of the children and can be asked to assume some light household tasks. 

In return, the host family offers free board and lodging as well as pocket money. However, the au pair is neither a housekeeper nor a nanny. 
The cultural exchange should be the main aim of an au pair stay. The au pair also has the opportunity to improve his or her language skills by attending a language course in the host country. He or she should however already have some basic language skills beforehand. In general, the au pair bears the costs for the language classes and assumes the travel costs as well.
 

For further information:

Au Pair Programmes
Au Pair A–Z
Security
Au Pair Stories