Eligibility rules are given on page 59 of the annotated rules:
One must be affiliated to a legal entity (see page 49 of the annotated rules for more details). Undergraduate students are not eligible. Master students need to provide a document signed by their university stating that they follow a master degree affiliated to a research programme.
One must be from a COST member country or a Near Neighbor Country (see the list below), unless one is invited to a school as trainer.
People not from a COST member country or a Near Neighbor Country can be funded once in the lifetime of the action to participate to a WG meeting but neither a school as trainee or an STSM.
COST member countries: Albania, Austria, Belgium, Bosnia and Herzegovina, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Georgia, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Republic of Moldova, Montenegro, The Netherlands, The Republic of North Macedonia, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey, Ukraine, and United Kingdom + Israel + South Africa.
COST Near Neighbor Countries: Algeria, Armenia, Azerbaijan, Belarus, Egypt, Jordan, Kosovo, Lebanon, Libya, Morocco, Palestine, Syria, and Tunisia.