Visa is required for citizens of France to visit Vietnam. French nationals may have 2 options: Visit Vietnam embassy in France or apply for a visa on arrival to Vietnam from France online. French citizens may apply for both tourist and business visa to Vietnam for the stay of 1 to 6 months from France. Please check this link for visa fee for French citizens.

All the information for getting a visa from Vietnam embassy in France can be found here: http://www.vietnamembassy-france.org/