This chapter shows just how deeply affected English has already been through its unprecedented spread, and the unique function it has as the world language. It argues, however, that it would be premature to launch into a discussion of the teaching of this lingua franca before certain prerequisites have been met. The most important of these are a conceptualization of speakers of lingua franca English as language users in their own right, and the acknowledgment of the legitimacy of, and indeed the need for, a description of salient features of English as a lingua franca (ELF), alongside English as a native language (ENL). The presentation summarizes the empirical research into the lingua franca use of English, which has recently gathered considerable momentum. It sets this research in relation to other relevant work in descriptive linguistics, sociolinguistics, and applied linguistics for language pedagogy. Finally, it discusses the implications of this historically unique situation for potential developments in the pedagogy of English teaching and outlines some research questions that must be addressed if advances in the teaching of English as a lingua franca are to have a secure theoretical and descriptive base.