Why? This is because Italy as we know it today did not exist until that date. On March 17, 1861 all people who were born in the territories which became Italy were automatically given Italian citizenship. If your ancestor was not alive on that date, s/he never was actually Italian. Pretty amazing to think, right? Also, if your ancestor had naturalized as a citizen of another country before that date, s/he never had a chance to obtain Italian citizenship.
2. Your last Italian-born ancestor did not naturalize (or never naturalized at all) as a citizen of another country before s/he had his or her child.
Let me explain with a hypothetical. Let’s say you are claiming Italian dual citizenship through your paternal grandfather (dad’s dad) who was born in Italy. Your grandfather must not have become a naturalized citizen of the United State (or any other country) before the birth of your father. This is because Italian citizenship is passed by way of jure sanguinis—Latin for “by right of the blood.” Thus, if your father was born to an Italian father, he was passed down with Italian citizenship. But, if your father was born to a dad who lost his Italian citizenship already by naturalizing before your dad was born, then the Italian citizenship did not get a chance to pass on.
3. Your last Italian-born ancestor must have naturalized after July 1, 1912.
This is the date that the current modern Italian citizenship law came into effect (with subsequent modifications and amendments, of course). It used to be that Italian consulates applied the law retroactively and allowed people to apply even if their ancestors naturalized before this date, but as of the time of this writing no consulate in the U.S. applies the law retroactively anymore.
People whose ancestors naturalized before this date may find luck applying in Italy, where many comuni apply the law retroactively.
4. If you have women in your line, their children must be born on or after January 1, 1948.
On this date, Italian women were finally given the right to pass down citizenship to their children. It’s crazy to think about, but up until this date when the Italian constitution came into force, women could not pass on Italian citizenship!
In a situation where you have a maternal relative of Italian descent, in order for you to apply via either a consulate or directly in Italy, your female relative must have had her child on or after January 1, 1948. Otherwise, you will be turned away.
However, all is not lost! The Italian courts have time and time again recognized the unfairness of this law. If you still want to obtain Italian dual citizenship but have what is known as a “1948 case” you can hire an Italian attorney to try the case for you in Rome. S/he will argue the unconstitutionality of the law. You do not need to be present in Italy for this, and can give them power of attorney for you. To date, these lawsuits have been very successful.