Book excerpt: This book presents intentional dynamics, which is a new perspective on TESOL contexts, activity and outcomes.The key innovation is a synthesis of complex systems and ecological theories, as well as the concept of intentionality from the philosophy of mind, to understand the psychological and social processes of TESOL. One aspect of intentional dynamics is the ‘ordinary’ intentions of individuals to perform particular actions, and of organisations to achieve planned outcomes. Another aspect is philosophically defined psychological and social forms of intentionality. Psychological intentionality is understood as what language learners' and teachers' (and other stakeholders') beliefs and emotions are ‘about’ or ‘directed at’. Social intentionality is the ‘aboutness’ expressed by TESOL materials, curricula and policies. The book explores how intentional dynamics both emerge from and give shape to TESOL activity, and outlines what are the practical implications of intentional dynamics for TESOL learners, teachers, researchers, managers and policy-makers.