Every short term rental in Italy must now carry a national identification code, the CIN, displayed on the listing and at the property itself. That is the one rule that holds everywhere.
Beyond it, the map fragments. Several European countries have introduced national limits on short term letting; Italy's government has resisted, with Deputy Prime Minister Matteo Salvini describing attempts to regulate the use of private property in those terms as unacceptable. That has left the work to city councils, with Florence first, producing a patchwork where the rules depend on which city you are standing in, and continuing court cases, often against the government, mean the position keeps moving.
For a guest, the practical consequence is limited but real. The rules are aimed at owners rather than visitors, so the risk is not a fine; it is a booking that turns out not to comply, in a city that has decided to enforce.
For the housing debate the fragmentation is the story. Cities carrying the cost of tourist pressure are the ones legislating, while the national government protects the owner's side of the transaction. Until that disagreement is settled, Italy has a national registration number and no national policy.