Katsouranis made his international debut for Greece on 20 August 2003 against Sweden and scored his first goal against Kazakhstan in a 2006 FIFA World Cup qualifier. Katsouranis was one of the key factors in Greece's triumph at UEFA Euro 2004, beating Portugal in his own "home" (Benfica's Estádio da Luz) and, following Greece's success at the tournament. Forced his way into the starting XI after coming off the bench for the opening game of the tournament, he was an extremely important part of a three-man midfield that also included Theodoros Zagorakis and Angelos Basinas. It was in Portugal that Katsouranis really made a name for himself, delivering a string of consistent performances culminating with that famous final in Lisbon. Lifting the Henri Delaunay trophy represents the pinnacle of a national-team career that so far has never again reached the same heights.