Linguistic complexity in second language acquisition

Since the 1990s linguistic complexity has become an important issue in second language acquisition (SLA) research and teaching: second language (L2) learners want to know how well they are progressing, while teachers and researchers are interested to find out which grade of complexity can be associated with a particular proficiency level. After a short sketch of the background to the construct of complexity, the paper presents an overview of how complexity is measured in SLA, how it is related to other constructs of language proficiency (in particular accuracy and fluency), and by which factors complexity may be affected: these concern both internal linguistic factors and external factors, like task-related features and type of instruction. The paper concludes with directions for future research, focusing on the need for non-redundant, valid and reliable measures, more developmental measures, a broader scope of complexity, combined cross-linguistic and longitudinal research, and more research in instructional practice.