There is no single permit for everyone. What you need depends on two things: your citizenship and your reason for staying. This page gives you the basic picture. It cannot tell you what applies to your case.
EU citizens
Citizens of EU countries can move to Italy freely. They do not ask for a permit to stay, but they usually must register their residence with the comune if they stay for longer than a short visit. The documents asked can vary, so check with the office.
Citizens of other countries
If you are not an EU citizen, you generally need the right visa to enter and then a permit to stay, called the permesso di soggiorno. There is a short deadline to ask for it after you arrive. Check it on the first day, because missing a deadline can cause problems.
The reason for staying matters
Work, study, family, retirement with own means, and other reasons each have their own rules, documents and rights. Two people with the same passport can have very different paths.
Where to check
- The Questura, the local police headquarters, handles permits. Ask them what applies to you.
- The Italian consulate in your country can explain the visa step.
- An immigration lawyer or a recognised advisory service can read your documents and give advice.
Do not rely on stories
Rules change, and offices do not always apply them the same way. What worked for a neighbour may not work for you. Always confirm with the Questura or a professional before you act, and write down the date you asked for each thing.