Every pet entering Italy needs a microchip that meets the ISO 11784/11785 standard — the international format most vets in the US, UK, Canada, and Australia already use, but it's worth double-checking with your vet if your pet was chipped abroad or years ago, since older or non-compliant chips can cause problems at check-in. A clearly readable tattoo applied before 3 July 2011 is still accepted as an alternative for older pets, but chips implanted after that date must meet the ISO standard — a tattoo alone is not enough for a newly chipped pet.
The detail that trips up more owners than anything else in this whole category: the microchip has to go in before the rabies vaccination, not after. If a pet was vaccinated first and chipped second, that vaccination doesn't count for travel purposes under EU rules, even if it's medically valid — the vet will need to give a new rabies shot after the chip is implanted, and the travel clock resets from that date.
The appointment itself is quick and low-drama — a chip about the size of a grain of rice, inserted under the skin between the shoulder blades, no anaesthesia required. Ask the vet to scan and confirm the chip reads correctly before you leave the clinic, and get the chip number written on any paperwork you're issued, since it needs to match exactly across the passport or Health Certificate, the rabies certificate, and the pet's collar tag if it has one.