The European Union Science Olympiad (EUSO) is a unique, multidisciplinary, integrated, Science, practical-based, team competition. It was established to provide young EU students with a platform to display their scientific capabilities. The concept of the EUSO thus developed from the senior Olympiads which existed at international level at the time. To be accepted by EU Science educators and governments, it would have to mirror these single subject, individual, theory-based Olympiads in several respects and yet be novel in aspects that embody and reflect new ways of teaching and learning. This thesis tracks the historical growth and success of the EUSO from its establishment in 2003 to the present day. It describes the background and significant difficulties involved in convincing EU Science educators of its merits. The philosophy, rationale, teething problems, evolution, integration and key role of team-work are outlined. The EUSO's contribution to the education system of today, and the performance of Irish students in EUSO in comparison to the performance of students from the old and new Europe, are examined. A crucial element in this success story has been the methodology used in the organisation of the EUSO: Participatory Action Research (PAR). Through this democratic process, participants were released from the constraints of the established Olympiad structures and enabled to function in an environment which allowed them to investigate their own reality in order to change it. Such actions have resulted in the development of a new science Olympiad model, the EUSO model. The EUSO has worked: 22 countries and 132 students participated in 2012. 906 students have taken part since 2003. The most striking finding in its ten year history, however, is the dominance of the gold and silver medal categories by the former Soviet Bloc countries.