If you wish to stay in Greece for more than 90 days, you need to apply for a residence permit as a family member of a Greek citizen. In order to do so, you will have to register your marriage in Greece before your arrival to Greece, if the marriage is not already registered here.
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How can the spouse of a Greek citizen reside in Greece for more than 90 days?
My wife was born in Greece and is a Greek citizen. She has a Greek Identity Card and Greek passport. I am an Australian national. We have our own unit in Greece. If we go to stay in our unit for an extended period when we retire, do I need a visa if we are going to stay longer than 90 days? If yes, what visa should it be?