Greece is a member state of European Union. Citizens of the EU countries may enter Greece with their ID card or passport.
Greece is a Schengen country. Thus, visa is not required among the citizens of the other countries of the Schengen Area.
The citizens of the non-Schengen member countries are requested a mandatory Schengen Visa in order to enter the Schengen Zone. The Schengen countries share common rules for issuing the Uniform Schengen Visa to transit or reside in the desired territory for a certain period of time up to the maximum of 90 days every six month period starting from the date of entry.
For further information please contact the Greek embassies or consulates. More here
The following consulates are located in Thessaloniki.