This book addresses a fundamental problem in applied social science and educational research: the widespread difficulty researchers and students from all disciplines face when trying to combine people-based and evidence-based research into complex social settings characterized by uncertainty and the unknown. More than ever, researchers need flexible means and grounded theory to inquire and step into challenging situations that do not lend themselves to straightforward technical explanations and solutions. The authors build on insights from many disciplines and lessons from the history of Participatory Action Research (PAR), French psychosociology and related fields. The ongoing evolution of PAR has had a lasting legacy in fields ranging from community development to education, public engagement, natural resource management, and organizational. All formulations have in common the idea that research must be done with people and not on or for people. Inquiry of this kind makes sense of the world through efforts to transform it, as opposed to simply observing and studying human behavior and people's views about reality, in the hope that meaningful change will happen somewhere down the road. The book contributes many new tools and conceptual foundations to this long-standing tradition, grounded in case studies and real-life examples of collective fact-finding and analysis from around the world. It provides a modular textbook on participatory action research and related methods, theory and practice, suitable for a wide range of undergraduate and postgraduate courses, as well as working professionals.