Action research is a form of reflective inquiry with intended use and users; practitioners in their own educational settings conduct it in order to improve their own professional practice and outcomes for students. Through action research, educators identify pressing problems of professional practice and engage in data collection, analysis, and interpretation, with the intention of understanding gaps between desired and actual results and achieving genuine improvements in the quality of their instruction and student learning. The action research process and resultant findings can equip practitioners with the knowledge they need to make real-time, evidence-based decisions about schooling, teaching, and learning. This entry discusses the development of action research as a method of inquiry, how and why action research is used in PreK–16 schools and barriers ...