My grandfather was born in Greece, 1/6/1901. His parents immigrated first to Canada, then New York when he was about 13. I would like to get a copy of his birth certificate so that I can apply for Greek citizenship, but I was told that his father's surname was changed at immigration. His mother's maiden name was Constantina Anavrides. His father's first name was Demetrius. I do not have a copy of their marriage certificate and I was only told they came from Sparta. George Chahalis died in April, 1983, in Riverhead, NY. My Mother is half Greek, half Irish. Do I have to have certified documents to apply for dual citizenship with USA and Greece?

You have enough information to make a legitimate search. Ideally, you will find his original last name from a passport or other document. But even without this information, the fact that you know a) his birth year, b) his father's name, and c) his mother's maiden name is good.

As a male Greek Citizen, your grandfather was inscribed in the Military Records of his municipality on the year of his birth. There are20 municipalities in the prefecture of Laconia [Sparta, and a number of smaller ones], so you or your lawyer will need to go to each of them with the information you have and identify the record that corresponds to your grandfather. It will be time consuming, but should be straightforward given the information you have.

Once you have found this certificate, you can prove that your grandfather was a Greek Citizen, and will then need his marriage cetificate to your grandmother, your mother's birth certificate, your mother's wedding certificate, and your own birth certificate.

There are some complications [prior to 1982, Greece only considered religious wedding ceremonies as valid, and not all religious weddings at that] but the primary thing for you would be to find that Municipality Certificate.

Best of luck.