Lots of questions out there, particularly from US resident tourists. Hopefully these websites help.
Italy’s current entry regulations: https://www.salute.gov.it/portale/nuovocoronavirus/dettaglioContenutiNuovoCoronavirus.jsp?lingua=english&id=5412&area=nuovoCoronavirus&menu=vuot
Entry info based on passport, origin and transit points, itinerary: https://infocovid.viaggiaresicuri.it/index_en.html
EU Green Pass: https://ec.europa.eu/info/live-work-travel-eu/coronavirus-response/safe-covid-19-vaccines-europeans/eu-digital-covid-certificate_en
US CDC card acceptedin lieu of EU Green Pass https://ambwashingtondc.esteri.it/ambasciata_washington/en/sala-stampa/dall_ambasciata/ingressi-in-italia-dagli-usa-e.html
And for Canadians: https://ambottawa.esteri.it/ambasciata_ottawa/it/ambasciata/news/dall_ambasciata/2020/03/focus-coronavirus.html (English translation button apparently not working but “ Le certificazioni vaccinali e di guarigione rilasciate dalle autorità sanitarie del Canada sono riconosciute come equivalenti alle certificazioni italiane” is what you need to know.
Apologies to residents of Japan for my inability to find a government site specifically confirming acceptance of your country’s vaccination certificate.
For the dPLF required for each adult (minor children to be listed on the form of their accompanying adult): https://app.euplf.eu/#/
Help re completing the dPLF: User manual for help completing the dPLF: https://www.salute.gov.it/imgs/C_17_pagineAree_5411_11_file.pdf
Italian National Tourism Authority guide to Covid-19 regulations: http://www.italia.it/en/useful-info/covid-19-updates-information-for-tourists.html
TA Italy forum “Coronavirus Situation” thread for daily updates re Italy’s situation and updates:: https://www.tripadvisor.com/ShowTopic-g187768-i20-k13238308-o10-Coronavirus_situation-Italy.html
If anyone knows of other sites that are missing please share.