This volume illustrates the high potential of learner corpus investigations for research into the CAF triad by presenting eleven original learner corpus-based studies which are set within solid theoretical frameworks, examine learner corpora with state-of-the-art analytical techniques and yield highly interesting findings. The volume’s major strength lies in the range of issues it undertakes and in its interdisciplinary thematic novelty. The chapters collectively address all three dimensions of L2 performance related to different linguistic subsystems (i.e. lexical, phraseological and grammatical complexity and accuracy, along with fluency) as well as the interactions among these constructs. The studies are based on data drawn from carefully compiled learner corpora which are analysed with the help of diverse corpus-based methods. The theoretical discussions and the empirical results shall contribute to the advancement of the fields of SLA and writing and speech research and shall inspire further investigations in the area of the CAF triad.