Citizens of EU countries and of Iceland, Liechtenstein, Norway and Switzerland do not need a student visa or a residence permit to study in Greece. For full details on required documents and procedures, visit the official AUTH page:
eurep.auth.gr/en/students/info/visa_residence
Visa
Students from non-EU countries must apply for a student visa before travelling to Greece. To do so, contact the nearest Greek Embassy or Consulate in your home country. You will need a Letter of Acceptance issued by the university, which will be sent to you by email and post after your registration is confirmed.
Residence Permit
If you plan to stay in Thessaloniki for more than 3 months, you must apply for a Residence Permit after your arrival. Applications are submitted in person at the Immigration Office of Thessaloniki (1, Taki Oikonomidi Street, tel: +30 2313 309202). The university will provide the certificates you need for your application.