The paper investigates the increasing number of international co-authored publications, comparing countries that accessed the European Union (EU) in 2004 (EU04) against other Central-Eastern European Countries (othEast-ERA), adopting a scientometric approach. This comparison looks at whether to be part of the EU is different from being part of the European Research Area (ERA) – given that both entities aim at fostering more international collaborations. The hypothesis is that EU might convey more opportunities for the sake of international publications, although ERA assures access to European funding schemes anyway. Analysing the census of internationally co-authored publications from 1995 to 2015, difference-in-differences regressions show that Countries that joined EU in 2004 performed better than other Central-Eastern ones. Implications for the public policies in science are discussed.