While the professional and methodological literature surrounding TESOL has, until recently, promoted monolingual, English-only approaches in the classroom, the deployment of multilingual resources and repertoires has long been a reality in many TESOL classrooms around the world. Although many teachers perceive a value in drawing on all the learners' own linguistic resources to support learning, the multilingual classroom has, until now, been an 'elephant in the room' in the professional discourse of the field. This chapter will therefore explore the realities of TESOL practice through the 'lens' of 'translanguaging'. Having established an understanding of translanguaging which underpins the subsequent discussion, the chapter traces the emergence of monolingual ideologies and approaches within the methodological literature of TESOL in the early twentieth century. It notes how the literature overlooked localized bi-and multilingual pedagogies, and the consequent gap between TESOL 'theory' and 'practice'. It then offers evidence of widespread contemporary multilingual classroom practices, drawing on both secondary sources and primary survey data documenting the practices and attitudes of teachers around the world towards monolingual teaching and translanguaging in the classroom. The chapter concludes with a call for further professional discussion of translanguaging, particularly in teacher training and education programmes, to facilitate teachers' professional development and support classroom practice.