Becoming more and more a multidisciplinary domain of study, the development of research in second language acquisition, and even more visibly in multilingualism, has moved away from its sole focus on cognitive aspects to social-affective dimensions. Consequently, research in these areas makes more extensive use of research methodology characteristic of social sciences. The focus on identity brings together issues of social context and the construction of one’s identity through negotiation of who we are, how we relate to the outside world and how we position ourselves in relation to others (Pavlenko 2001). Language is the main tool in this construction/negotiation through the acquisition/learning and use of multiple languages. In relation to the development of one’s multilingual identity, the major distinction has to be made between acquiring a language in its natural context (the case of one’s mother tongue or immigration) and learning it in formal contexts. Block (2014) believes that the issue of identity can only be studied in a natural environment of language acquisition, and not in a formal instruction context. This article aims to confirm or reject the above belief, based on evidence from various studies of bi- and multiple language users and how they perceive their identities and their relation to the languages in their possession. It includes a pilot study of trilingual language learners and their understanding of how the individual languages they know (L1, L2, L3) build their identities and the way they enrich, impoverish or challenge who they see themselves to have been by birth (Gabryś-Barker 2018). The issues discussed relate to external (other people, situations, contexts) and internal identity-building factors (individual affectivity, personality features).