This chapter examines, in a critical way, four different notions encountered in certain strands of academic discourse about multilingualism, which have acquired an influential position in some segments of contemporary applied linguistics. The four notions reviewed here are “superdiversity”, “languaging”, “commodification”, and “English as a lingua franca (ELF)”. The argument made in this chapter is that, while each of these concepts is problematic on its own, their combination gives rise to particularly problematic implications for language policy. The policy stances that can be derived from those notions are potentially harmful on allocative and distributive grounds, since they may undermine both linguistic diversity and linguistic justice. This chapter shows why they should be avoided, or at least substantially amended, in order to formulate policy responses aiming at the preservation of a genuine, sustainable and fair multilingualism. While the very use of these four notions raises questions regarding the evolution of applied linguistics, investigating them also matters to social scientists working on language issues, particularly language policy. The reason for this is that social scientists need to rely on sound analytical constructs in order to come to grips with the complexity of language and multilingualism as research objects, and as areas in which actual policies are selected, designed, implemented and evaluated.