Monolingualism, native-speakerism and standard language ideology have been identified as dominant ideologies in language teaching with severe effects on second language teacher identities. Such ideologies offer alleged certainties but also detach teachers from the actual uses and value of language in multilingual and multidialectal contexts. As a consequence, educators might feel constrained by rigid linguistic norms, hindering their capacity to re-evaluate their approaches to accommodate the diverse linguistic realities and communicative needs of English learners in an increasingly interconnected and multilingual global landscape. This chapter intends first to offer a broad perspective of how these ideologies have shaped language teaching and how they have clashed with research-based observations of multilingual and multidialectal communicative settings. We will give an overview of the relevant literature, ranging from foundational texts to more recent ones challenging the ‘ideal’ monolingual native speaker, and we will show how the above ideologies are still found in a rather pervasive way in the language teacher profession. This will be followed by an account of recent research conducted in teacher training environments aimed at showing ways to successfully gear future language teachers towards a new vision of language that contemplates diversity and hybridization as fundamental pillars on which teachers’ identities need to be based.