Third or Additional Language Acquisition critically examines the evidence available keeping two main questions in mind. The first is whether multilinguals should be considered as learners and speakers in their own right and, consequently, whether the distinction between Second Language Acquisition and Bilingualism, and Third or Additional Language Acquisition and Multilingualism is fully warranted. The second is how proficient in a non-native language learners are supposed to be before they can begin to be classified as multilingual learners in empirical research.