English as a lingua franca (ELF) refers to ‘any use of English among speakers of different first languages for whom English is the communicative medium of choice, and often the only option’ (Seidlhofer, 2011, p. 7Footnote *). ELF research started relatively recently. It was only discussed occasionally in the last century. Landmark changes were the publications of Jenkins (2000Footnote *) and Seidlhofer (2001Footnote *). These works inspired more research into ELF, as witnessed by a dramatically increased interest in ELF since then, resulting in a large number of journal articles, monographs, edited books (e.g. Mauranen & Ranta, 2009Footnote *) and large corpora (e.g. the Vienna-Oxford International Corpus of English, the Corpus of English as a Lingua Franca in Academic Settings, and the Asian Corpus of English). In addition, ELF researchers have launched the annual conference series (International Conference of English as a Lingua Franca), the Journal of English as a Lingua Franca, and the De Gruyter book series Developments in English as a Lingua Franca. These publications move from an initial understanding of ELF as a ‘variety’ or ‘varieties’ to a later conceptualisation of ELF as a dynamic, fluid and variable phenomenon. ELF has become a major focus of discussions and activities among both applied linguists and English language teaching professionals (Jenkins, Cogo, & Dewey, Reference Jenkins, Cogo and Dewey2011).

Therefore, in addition to Jenkins et al.'s (2011) state-of-the-art review of development in research into ELF in Language Teaching, a research timeline on ELF is needed. It would help readers perceive an up-to-date view of the field, understand the key developments in ELF research, and keep up with the latest studies since Jenkins et al.'s review. To achieve this goal, we attempted to systematically select works which best represent developments in ELF from among a plethora of studies which have been published up to 2018.

In this research timeline, there are 59 entries, including 13 monographs, 6 edited books, 1 chapter, and 39 journal articles. Items are annotated with one or more of the following coding categories:

1. A. Context

   1. 1. Academic

   2. 2. Business

2. B. Mode

   1. 1. Spoken

   2. 2. Written

3. C. The nature of ELF interactions

   1. 1. Phonological level

   2. 2. Lexicogrammatical level

   3. 3. Pragmatic level

4. D. Theoretical implications

   1. 1. ELF/ENL (English as a native language)

   2. 2. ELF/EFL (English as a foreign language)

   3. 3. ELF/EIL (English as an international language)/WE (World Englishes)

   4. 4. Identities and attitudes

5. E. Pedagogical implications

   1. 1. Teaching and learning

   2. 2. Testing

   3. 3. Teacher education

The first three categories – context, mode and the nature of ELF interactions – were derived from Jenkins et al.'s (2011) review. In their paper, Jenkins et al. organised ELF research by linguistic levels and domains. First, they categorised the major findings of ELF research into phonological, lexical/lexicogrammatical and pragmatic levels. Then, they proposed two highly investigated domains of social contact – business and higher education. Therefore, in our timeline, context was further distinguished into academic and business categories (A1 and A2), and the nature of ELF was divided into phonological, lexicogrammatical and pragmatic levels (C1, C2 and C3 respectively). As for the mode, there are spoken and written subcategories (B1 and B2 respectively). Written language has been comparatively less examined than spoken language in ELF research. The category D, theoretical implications, includes publications which have discussed similarities and differences between such terms as ELF, ENL, EFL and WE, attitudes towards ELF from various perspectives, or ELF speakers' perceptions of their identities. Category E, pedagogical implications, is dedicated to insights offered primarily by empirical research into how to apply ELF in teaching, learning, testing and teacher education.