Citizens of France won’t need a visa if stay for less than 15 days. A gap of at least 30 days between two visa-free visits is required.

You should apply for a visa if intending to stay for more than 15 days OR not meet the requirement of “a gap of at least 30 days between two visa-free visits is required”.

Under a government directive released in January 2017, citizens from 40 countries will be eligible to apply for the e-visa (30 days, single entry), including citizens of France. Therefore French passport holders now can apply online for e-visa (30 days, single entry) at the official website of the government of Vietnam.

What if a French passport holders wish to stay in Vietnam for more than 30 days or want to visit the country multiple times?

In case you want stay more than 30 days or want multiple entry visa for Vietnam, you are advised to contact with a company in Vietnam to ask for their arrangement for picking up your visa on arrival. There is a visa issuing office located at the international airport where you can show the visa approval letter (pre-arrangement) to pick up your visa there.

There are many websites arrange visa approval letter for picking up visa on arrival, you just need to choose a reliable one with best price to apply.