Greece is a member of the European Union and is part of the Schengen agreement. These two memberships define the visa requirements of foreign citizens seeking to visit Greece.
Schengen visa is required when you want to visit one or more countries in the Schengen area. (Austria, Belgium, Denmark, Finland, France, Germany, Iceland, Italy, Greece, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, Poland, Slovenia, Slovakia, Czech Republic, Malta, Estonia, Lithuania, Latvia and Hungary).