Whilst looking up the formalities for exchanging driving licences, I happened on a (to me) previously unknown bit of French bureaucracy - the Attestation d'accueil.
Apparently, you should apply for one of these if someone from outside the EEA + Switzerland is going to stay with you for a family or social visit. In theory, this means that I should have applied, & paid €30.00, when our Melbourne friends were staying with us. The fact that Australians, (or North Americans or ...) don't need a visa is, apparently irrelevant. Your mairie has to be satisfied that you can provide adequate accommodation & sanitary arrangements for your visitors. This sounds like a wonderful makework scheme, although it probably costs even more than €30 to administer. In practice, this must surely be legislation that is honoured mainly in the breach.
See this site for the gory details.