In France, a pacte civil de solidarité (English: "civil pact of solidarity") commonly known as a PACS, is a form of civil union between two adults (of the same or opposite sex) for organising their joint life. It brings rights and responsibilities, but less so than marriage.

The acronym has generated the French verb pacser.

It was introduced by the government of Prime Minister Lionel Jospin in 1998 to be a marked improvement and alternative over the previous certificat de concubinage notoire, which had been restricted to heterosexual couples and had been seen as having pejorative overtones. The situation of concubinage only made certain benefits extend to the other partner in a union, and did not settle any issue regarding property, taxes, etc...

Initially, PACS opened the right to file joint income taxes only after 3 years of a stable PACS. In 2005, for the first time, all PACSed couples are to file joint taxes, in the same manner as married couples. In France, a couple filing joint income taxes, in almost all cases, pays less tax than two singles if one of the partners earns substantially more than the other, due to the way that the progressive tax is applied.

On 5 June 2004 Noel Mamere, Mayor of Begles and a Green member of parliament, performed a wedding ceremony for Bertrand Charpentier and Stephane Chapin, purporting to unite them in marriage, not merely in civil union. The ceremony took place despite being forbidden by Prime Minister Jean-Pierre Raffarin, and warnings by Interior Minister Dominique de Villepin that the mayor would face legal action, including possible suspension from office. It remains to be seen if the marriage would be recognized as a marriage.