We begin by considering how the recent phenomenon of English as a Lingua Franca (henceforth ELF) fits in with the older notion of lingua francas in general as well as with older versions of ELF. We then explore the beginnings of ELF in its modern manifestation, including the earliest ELF research, and tackle the thorny issue of defining ELF. After discussing the main locations and domains in which ELF research has been carried out to date, we move on to examining research into three linguistic levels, lexicogrammar, phonology and pragmatics, concluding with a discussion of very recent findings revealing ELF's linguistic fluidity. Next, we discuss research into two domains where ELF has proved especially prevalent: business English and academic English. This is followed by a consideration of ELF as a globalized and globalizing practice. We end the article by exploring the implications of ELF research for ELF-oriented English teaching and the role that attitudes are likely to play in this. We conclude that while the relaxed attitudes towards ELF of younger people are promising, strong resistance is still felt by many others, and that the major challenge remains in convincing the examination boards that they should take account of ELF.