The main objective of this talk is to introduce the construct of phraseological complexity (Paquot, 2019) and illustrate its usefulness for language assessment. Phraseological complexity is defined in terms of the sophistication and diversity of word combinations and corpus-based metrics are used to operationalize these two dimensions. The talk will illustrate how this approach has been used so far to describe English Foreign Language (EFL) learner language development in cross-sectional and longitudinal studies (e.g. Paquot, 2018; Paquot et al., forthcoming). It will also identify major methodological challenges and sketch out directions for future research. References Paquot, M. (2018). Phraseological Competence: A Missing Component in University Entrance Language Tests? Insights From a Study of EFL Learners’ Use of Statistical Collocations. Language Assessment Quarterly 15:1, 29-43, DOI: 10.1080/15434303.2017.1405421 Paquot, M. (2019). The phraseological dimension in interlanguage complexity research. Second Language Research, 35(1), 121–145. https://doi.org/10.1177/0267658317694221 Paquot, M., Naets, H. & S. Th. Gries. (forthcoming) Using syntactic co-occurrences to trace phraseological complexity development in learner writing: verb + object structures in LONGDALE. In Le Bruyn, B. & Paquot, M. (eds.). Second Language Acquisition and Learner Corpora. Cambridge University Press.