This Element is a guide to task-based language teaching (TBLT), for language instructors, teacher educators, and other interested parties. The work first provides clear definitions and principles related to communication task design. It then explains how tasks can inform all stages of curriculum development. Diverse, localized cases demonstrate the scope of task-based approaches. Recent research illustrates the impact of task design (complexity, mode) and task implementation (preparation, interaction, repetition) on various second language outcomes. The Element also describes particular challenges and opportunities for teachers using tasks. The epilogue considers the potential of TBLT to transform classrooms, institutions, and society.