Participatory action research (PAR) is an approach to action research emphasizing participation and action by members of communities affected by that research. It seeks to understand the world by trying to change it, collaboratively and following reflection. PAR emphasizes collective inquiry and experimentation grounded in experience and social history. Within a PAR process, "communities of inquiry and action evolve and address questions and issues that are significant for those who participate as co-researchers". PAR contrasts with mainstream research methods, which emphasize controlled experimentaction, statistical analysis, and reproducibility of findings.

PAR practitioners make a concerted effort to integrate three basic aspects of their work: participation (life in society and democracy), action (engagement with experience and history), and research (soundness in thought and the growth of knowledge). "Action unites, organically, with research" and collective processes of self-investigation. The way each component is actually understood and the relative emphasis it receives varies nonetheless from one PAR theory and practice to another. This means that PAR is not a monolithic body of ideas and methods but rather a pluralistic orientation to knowledge making and social change.

In the UK and North America the work of Kurt Lewin and the Tavistock Institute in the 1940s has been influential. However, alternative traditions of PAR begin with processes that include more bottom-up organising and popular education than were envisaged by Lewin.

PAR has multiple progenitors and resists definition. It is a broad tradition of collective self-experimentation backed up by evidential reasoning, fact-finding and learning. All formulations of PAR have in common the idea that research and action must be done 'with' people and not 'on' or 'for' people. It counters scientism by promoting the grounding of knowledge in human agency and social history (as in much of political economy). Inquiry based on PAR principles makes sense of the world through collective efforts to transform it, as opposed to simply observing and studying human behaviour and people's views about reality, in the hope that meaningful change will eventually emerge.

PAR draws on a wide range of influences, both among those with professional training and those who draw on their life experience and those of their ancestors. Many draw on the work of Paulo Freire, new thinking on adult education research, the Civil Rights Movement, South Asian social movements such as the Bhumi Sena, and key initiatives such as the Participatory Research Network created in 1978 and based in New Delhi. "It has benefited from an interdisciplinary development drawing its theoretical strength from adult education, sociology, political economy, community psychology, community development, feminist studies, critical psychology, organizational development and more". The Colombian sociologist Orlando Fals Borda and others organized the first explicitly PAR conference in Cartagena, Colombia in 1977. Based on his research with peasant groups in rural Boyaca and with other underserved groups, Fals Borda called for the 'community action' component to be incorporated into the research plans of traditionally trained researchers. His recommendations to researchers committed to the struggle for justice and greater democracy in all spheres, including the business of science, are useful for all researchers and echo the teaching from many schools of research:

PAR can be thought of as a guiding paradigm to influence and democratize the creation of knowledge making, and ground it in real community needs and learning. Knowledge production controlled by elites can sometimes further oppress marginalized populations. PAR can be a way of overcoming the ineffectiveness and elitism of conventional schooling and science, and the negative effects of market forces and industry on the workplace, community life and sustainable livelihoods.

Fundamentally, PAR pushes against the notion that experiential distance is required for objectivity in scientific and sociological research. Instead, PAR values embodied knowledge beyond "gated communities" of scholarship, bridging academia and social movements such that research and advocacy — often thought to be mutually exclusive — become intertwined. Rather than be confined by academia, participatory settings are believed to have "social value," confronting epistemological gaps that may deepen ruts of inequality and injustice.

These principles and the ongoing evolution of PAR have had a lasting legacy in fields ranging from problem solving in the workplace to community development and sustainable livelihoods, education, public health, feminist research, civic engagement and criminal justice. It is important to note that these contributions are subject to many tensions and debates on key issues such as the role of clinical psychology, critical social thinking and the pragmatic concerns of organizational learning in PAR theory and practice. Labels used to define each approach (PAR, critical PAR, action research, psychosociology, sociotechnical analysis, etc.) reflect these tensions and point to major differences that may outweigh the similarities. While a common denominator, the combination of participation, action and research reflects the fragile unity of traditions whose diverse ideological and organizational contexts kept them separate and largely ignorant of one another for several decades.