National Health Service
Plain English
It's Italy's national public health service. Once you're enrolled, basic care is either free or very cheap: GP visits, hospital stays, emergency care, and most specialist visits. You enrol at your local ASL, and you can pick a family doctor at the same time.
Why it matters
If you have a work or family residence permit, SSN enrolment is mandatory and tied to your permit. For some other permit types (study, elective residency), you can voluntarily enrol by paying an annual fee.
Real example
"On her third week in Palermo, Mariana walked into her ASL with her permesso, codice fiscale, and proof of address. She picked a GP from a printed list, signed up to the SSN, and got her tessera sanitaria in the post a few weeks later."
Common confusion
Private insurance and the SSN are not interchangeable. Private insurance can speed up specialist visits, but only the SSN gives you full public-hospital coverage at the national rate.
Official source
Ministero della Salute