isla (print) issn 2398–4155 isla (online) issn 2398–4163 isla vol 3.2 2019 119–123 ©2019, equinox publishing doi: https://doi.org/10.1558/isla.37977 Instructed Second Language Acquisition Editorial Linguistic complexity and instruction in second language acquisition: introduction Folkert Kuiken, Ineke Vedder and Marije Michel Tis special issue investigates the interaction between the development of linguistic complexity, referring to the degree of elaboration, size, breadth, width, or richness of the learner’s L2 system, and pedagogical instruction in a second language (L2) . Te rationale behind the volume is to contrib- ute towards bridging the gap between research and classroom practice. Te issue draws on the conviction that theory and research fndings may ofer teachers deeper ways of understanding L2 learning and their own classrooms, and may encourage them to explore alternative pedagogical approaches. Conversely, teachers’ refections on what works in the class- room – and what does not and why – may give researchers more insight into language learning ‘in the wild’, leading to new research questions. Te contributions contained in this volume (fve research papers and one fnal commentary) all aim to identify, from diferent theoretical and empirical perspectives, the efects of various types of pedagogical interven- tion on the development of syntactic, morphological, and lexical complex- ity. Te following issues are addressed: (a) the impact of diferent types of instruction on complexity; (b) developmental trajectories of complex- ity; (c) diferential efects of task, genre and modality on complexity; (d) measurement and assessment practices of complexity in L2 instruction; e) teachers’ perceptions of complexity. 1 Afliations Folkert Kuiken: University of Amsterdam, Netherlands. email: f.kuiken@uva.nl Ineke Vedder: University of Amsterdam, Netherlands. email: i.vedder@uva.nl Marije Michel: University of Groningen, Netherlands. email: m.c.michel@rug.nl