In France all civil act are freely available.
Each department has his own archive internet site. If you don't know the department number go on Google or Wikipedia, you will get the department number of the searched town.
Acts older than 100 years :
birth, marriage and wedding acts are freely online for everybody without any restriction
Some town gives acts until years 1940.
For act which are not online on archive sites :
Yeach town hall has his civil act service. You can send a form to ask for a civil act. It will be sent freely all around the world.
there are some restrictions :
If the person who demand the act is himself, his parents or his children : no restriction.
For other peoples :
birth act : you get his first name(s), his last name and wher he is born. If he has been married : you get also the name of the partner, the town of the wedding. If he is divorced, the date of the act of divorce. All thes informations are available for all marriages he has got.
wedding act : the name of both partner, date and town of the act. If there is a divorce, the date of the act is displayed.
death act : no restrictions, you get the birth infos as in the birth act and the name of his parents, the date and the town of death.
Take care : some private companies may ask you to pay for asking these acts. All these acts are freely available.
All thes acts are freely sent by the towns halls all round the world.
Just a limit : all forms for asking the acts are written in french. You can get an automatic translation with Google Translate.
When looking for a particular marriage record in the Paris online archives (http://archives.paris.fr/s/4/etat-civil-actes/?), recently, I was reminded that this is a fantastic resource but it seems to be little known. You have to browse by date and arrondissement, and (of course) the records are all in French, but they are original records that are free to view and free to download. Apart from the date and place of the civil ceremony, the marriage records (potentially) contain a great deal of useful information about the bride and groom, including DoB and place, their occupation, and addresses, and their parents' names, occupations and addresses; there's even some info about the witnesses. In addition, if they have received subsequent notification of the dissolution of the marriage, that, too, will be noted.
When looking in the 1940s, there were a significant number of Allied Forces personnel. There are even records affirming marriages conducted in prison camps.