Tasks are viewed as a principled foundation for classroom teaching, social interaction, and language development. This special issue sheds new light on how task-based classroom practices are supported by a diverse range of principles. This introduction describes current trends in classroom practice and pedagogic research in relation to task-based language teaching (TBLT), offering a rationale for revisiting the TESOL profession's understandings of the uses of tasks in language classrooms. It then summarizes the contributions appearing in this issue, which address topics including: interaction in task planning and completion, the use of tasks to support writing development, learner perceptions and interpretations of tasks, and the relationship between autonomy and TBLT. Collectively, these contributions advance complementary theoretical perspectives on classroom learning and teaching in diverse EFL and ESL settings. Overall, they reflect the broadening scope of second language acquisition theory while maintaining a tight focus on classroom realities.