This dissertation investigates the theoretical premises and pedagogical implications of plurilingualism through an extended analysis of the academic and (where appropriate) policy literature. Firstly the tension between superdiversity, caused by globalisation, at the social and individual levels, is juxtaposed with traditional approaches to language teaching. Two main forces in traditional language teaching, a monolingual ideology and cognitive second language acquisition (SLA) are examined. By exploring the profound influence of monolingual ideology over language classrooms, the research brings to the fore the need for a new theoretical framework in the field of language education. The investigation raises influential recent shifts in the language field, particularly the “social turn” and the “multilingual turn”.

Subsequently, the theoretical premises and core concepts of plurilingualism are carefully investigated, aiming to identify the difference between this new lens and traditional language education. When the research explains possible practices of plurilingual education, two different pictures are presented. On the one hand, in many pluralistic language classrooms where this new perspective is embraced, teachers have achieved gratifying results in developing students' plurilingual and intercultural repertoires and cultivating their composite competence. On the other hand, the research also shows that many language teachers lack awareness of the use and further development of students' whole linguistic and cultural repertoires. In the meantime, some disconnection between theoretical knowledge and practice is caused by inadequate pre service and in service professional development and training.

After an in-depth analysis of its characteristics and advantages, this research identifies that although plurilingualism has not yet become an accepted theory of language in mainstream language education, this action-oriented, student-centred pedagogical approach and its broad and strategical framework can provide high-quality language education in an era of superdiversity. In addition to cultivating students' plurilingual and intercultural ability, it can also foster lifelong learning awareness of the need to continue to cultivate these skills and understanding. Finally, this dissertation also analyses the key points, difficulties, and possible solutions of promoting plurilingualism in schools.

This research suggests that many educators and language teachers still lack awareness of the implication embodied in this new concept or lack adequate support for implementing it in the classroom setting. It is necessary to address these issues through professional training. In addition, studies on experiences of schools that have successfully shifted from traditional pedagogy to pluralistic approaches would be helpful.