Action research focuses simultaneously on action and research. The action aspect requires some kind of planned intervention, deliberately putting into place concrete strategies, processes, or activities in the research context. Interventions in practise are usually in response to a perceived problem, puzzle, or question that people in the social context wish to improve or change in some way. These problems might relate to teaching, learning, curriculum or syllabus implementation, but school management or administration are also a possible focus. This chapter describes the origins of action research, its relationships to other forms of empirical research, its reach and development, its central characteristics, and the current debates that surround it. It also considers the scope of action research in the applied linguistics field and concludes by looking at future directions.