Before you start

A residence permit or validated visa
Proof of stable residence in France
An employment contract or proof of activity, for the fastest route
A French RIB, for reimbursements

Step-by-step

1
Start the social security registration in your first week
If you are employed, your employer initiates it, but the process is slow and you should track it rather than assume it is moving. The number is what everything else hangs off. Expect months rather than weeks and do not read the delay as a sign something has gone wrong.
Via employerWho: You and your employerWeek 1
2
Keep every feuille de soins until the card actually works
Until the carte Vitale arrives you pay in full and the practitioner gives you a paper claim form. Keep all of them — once your file is active they are reimbursed retroactively, and people routinely lose several hundred euros by discarding paperwork that appeared to be going nowhere.
In personWho: You
3
Declare a médecin traitant in your first weeks and ask people rather than directories
Naming a family doctor with the fund raises your reimbursement rate permanently and is the gateway to specialists. Practices in and around Nantes close their lists, and a personal referral from a colleague or neighbour opens doors a directory search does not.
In personWho: YouWeek 1–4
4
Take the employer mutuelle unless you have a specific reason not to
The state reimburses most but not all of a consultation and covers dental and optical care poorly. Employers are generally required to offer a complementary scheme and to fund at least half of it. Almost everyone in France carries one.
Via employerWho: You
5
Create an Ameli account as soon as you have a number
The online account is where reimbursements, your card status and the attestation de droits live. That attestation is another document you will be asked for repeatedly, by employers, schools and insurers.
OnlineWho: You
6
Check which CHU site your specialist is on before travelling
The university hospital is consolidating its sites into a single new building on the Île de Nantes, targeted for the late 2020s. Departments move on their own timetables in the run-up. Confirm the address on the appointment letter each time rather than going where you went last year.
OnlineWho: You

Documents you’ll need

Residence permit or validated visa
Birth certificate with a sworn translation, frequently required
Employment contract or proof of activity
Justificatif de domicile
RIB for reimbursements

Things most newcomers don’t know

Keep every paper claim form from your first months — they are literally money.

Before the carte Vitale arrives you pay in full and receive a feuille de soins to submit on paper. Once your file is active those claims are reimbursed retroactively, sometimes many months later. New arrivals discard them because nothing appears to be happening, and then cannot reconstruct several hundred euros of legitimate reimbursement they were entitled to.

Source: l'Assurance Maladie

Not declaring a médecin traitant costs you on every single consultation, indefinitely.

The reimbursement rate inside the coordinated care pathway is substantially higher than outside it, and you are outside it until you have formally named a family doctor with the fund. That is a permanent penalty rather than a one-off, and it applies from your first visit. Treating it as a first-month task rather than a first-illness task is the difference, particularly where practice lists are closed.

Source: l'Assurance Maladie

A translated birth certificate is the single most common reason a registration file sits still.

French social security registration frequently requires a full birth certificate, sometimes recently issued, translated by a court-approved sworn translator. Obtaining one from another country takes weeks, and the requirement rarely surfaces until the file is already open and waiting. Start it before you leave rather than when the caisse asks for it.

Source: l'Assurance Maladie

For anything non-urgent out of hours, the number to know is not 15.

The SAMU line at 15 is for genuine emergencies and calling it for a fever on a Sunday clogs a system people depend on. France runs a separate out-of-hours GP access number, 116 117, for exactly that situation, and pharmacies operate a rota with the on-duty pharmacy posted in the window and online. Knowing which of the three to use is the difference between an hour and a night.

Source: l'Assurance Maladie

Common mistakes to avoid

Discarding paper claim forms before your social security file is active.
Leaving the search for a médecin traitant until you are actually ill.
Arriving without a translated birth certificate and stalling registration for weeks.
Declining the employer mutuelle without understanding what the state does not cover.
Turning up at last year's CHU site while departments are moving to the new hospital.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.