When you have decided to apply for italian citizenship. Documentation requirements may vary slightly from consulate to consulate, but the following documents are required to support your application.
Birth Certificate of the "Commune" in Italian
You will need a birth certificate for your Italian ancestors born in the commune of Italy where they were born. In the event when you are claiming Italian heritage based on grandparents on the father's side, you will need a certificate for both grandparents from each commune and for your parents.
In short, you will need a birth certificate for every generation in a lineage directly to you. To get more information regarding documents needed for italian citizenship you may go through https://getitaliancitizenship.com/italianrecords/.
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If the ancestors of Italy die, you will need a copy of the appropriate official death certificate. Also, this document should be supported by an apostille and translated into Italian. In certain cases it may take note of death.
Certificate of Marriage from Italy
As with the birth certificate, you must obtain a marriage certificate outlining that both of your parents, grandparents, great grandparents, or great great grandparents were married in Italy.
If the wedding is taking place in the United States, you will need an official copy of the marriage certificate along with an apostille from the relevant Secretary of State.