This course will examine several forms of linguistic diversity at the individual and community level as well as their impact on language and identity construction. Through the class, students will discuss and understand the emerging notion of plurilingualism as distinct from multilingualism and analyze it from three different scientific points of view: cognitive, sociological/sociocultural and pedagogical. The course will adopt a global perspective in investigating language diversity and its implications in different geographical areas and historical times. The course is at doctoral level but it is open to Master's students (with permission of the instructor).