This volume consists of a collection of empirical studies and research syntheses investigating the role of individual difference (ID) variables in task-based language teaching (TBLT)—a pedagogical approach that emphasizes the importance of the performance of meaning-oriented tasks in facilitating second language learning. TBLT is subject to learner-external as well as learner-internal factors, with the former referring to task- and context-related factors, and the latter to ID factors pertaining to learner traits, dispositions, or propensities. To date, the research has focused primarily on learner-external factors, and there has been insufficient and unsystematic research on individual difference factors. This volume brings centre stage this important but under-researched dimension by means of a comprehensive, in-depth examination of the role of key ID factors in TBLT. The volume integrates theory, research, and pedagogy by spelling out the mechanism through which IDs influence learning attainment, behaviours, and processes, examining evidence for theoretical claims, and discussing ways to apply research findings and cater to individual differences in the task-based classroom.