In the context of the Lisbon Strategy and the "Education and Training 2010" plan, the plurilingualism of European citizens is a high priority. Currently, due to its historical and cultural background, as well as the pace of its development, the European Union with its 27 member states (EU-27) is a mosaic of official languages where multilingualism is often encountered, notably due to the small size of certain territories and the proliferation of linguistic borders. The stated objective that every European citizen possesses linguistic skills in two European living languages other than their mother tongue is very ambitious but is certainly a necessary condition for the generalization of exchanges among the five hundred million Europeans. The first people targeted are those involved in European commerce. If the EU-27 wants to become an area of strong economic growth, all aspects allowing for an improvement in intra- and extra-community trade must be highlighted. Plurilingualism is one of the major factors facilitating this objective. The observation of the geographical map of Europeans' plurilingual capacities reveals three zones: a "north" zone where these capacities would be important, a "central" zone where they would be moderate, and a "south" zone where they would be weak. A representative from the aforementioned zones, namely the Netherlands for the first, France for the second, and Spain for the last, has been chosen. Divided into three parts, this thesis presents the language policy in Europe, an analysis of the use of English in the professional and private lives of French citizens, and a state-of-the-art review of English language certifications, with a final study and proposal of a diagnostic assessment of language abilities tested on two cohorts of students in France and Spain.