The inextricable and interdependent link between language and identity has long been acknowledged (e.g. Joseph 2004; Norton 2000). Language is, after all, the means through which we identify ourselves and are, in turn, identified by others. Yet, we live in an increasingly multilingual world where many individuals have multiple languages in their repertoire. It is important to note that we use the term ‘multilingual’ here in its broadest sense, to include learners who have knowledge of more than one language, regardless of their level of proficiency in their languages or how they were acquired; we include not only spoken languages, but also non-verbal forms of communication such as sign languages. Our position is that each language that is part of an individual’s repertoire may influence the nature of their identity negotiation in important ways. However, this raises significant questions about the relationship between multilingualism and identity and, in particular, the influence that this may have on language learning in a range of different contexts. For example: How do we conceptualise and research multilingual identity? How does multilingual identity intersect with other key constructs from the field of language learning, such as language beliefs and motivation, language emotions and intercultural understanding? What are its intersections with psychological constructs such as memory, and how are our memories and multilingual identities shaped by our social and cultural experiences? How can a better understanding of multilingual identity extend our existing knowledge of language learning and enhance language pedagogy? These are just some of the questions at the heart of this special issue.