Anybody who takes up residence in Austria (Austrians, EU/EEA nationals, nationals of third countries) has to register at the registration office their place of residence within three working days. You are required to fill in a registration form (“Meldezettel” - Meldezettel ), have it signed by the landlord/landlady and hand it in at the registration office.
If you stay in a hotel, you will be registered automatically by the hotel when checking in.
EEA citizens and people from Switzerland do not require a visa and have a right of residence in the Austrian federal territory for a period of up to three months. If you are an EEA citizen or from Switzerland staying in Austria for more than three months, you have to inform the responsible registration office in Austria in person within the first four months of your stay in Austria and apply for a registration certificate ("Anmeldebescheinigung").
For more information about these registration procedures see: registration office.