Cultivated within the long history of psychological research dedicated to social action, this chapter traces one stream of action research, critical participatory action research (critical PAR), across the 20th and the 21st centuries in the field of psychology. Rooted in notions of democracy and social justice and drawing on critical theory (feminist, critical race, queer, disability, neo-Marxist, indigenous, and poststructural), critical PAR is an epistemology that engages research design, methods, analyses, and products through a lens of democratic participation. Joining social movements and public science, critical PAR projects document the grossly uneven structural distributions of opportunities, resources, and dignity; trouble ideological categories projected onto communities (delinquent, at risk, damaged, innocent, victim); and contest how "science" has been recruited to legitimate dominant policies and practices.In the following pages, we sketch an intentional history of the seeds of critical participatory research as they have been nurtured, buried, and then rediscovered throughout the past century of social psychology. We then turn, in some detail, to Polling for Justice, a contemporary piece of quantitative and qualitative social inquiry, designed as a participatory survey of and by youth in New York City with adult researchers, poised to track social psychological circuits of injustice and resistance as they affect the educational, criminal justice, and health experiences of urban youth (Fox et al., 2010). We purposely focus on a very traditional psychological methodthe self-completed questionnaire-to illustrate how methods, analyses, and products shift when engaging critical PAR as an epistemology. The chapter closes with a discussion of critical science to make explicit the validity claims of critical PAR.The history of critical PAR has been told through different legacies. Within education studies, critical PAR is associated with the tradition of liberation theology and Paulo Freire. Within postcolonial studies, critical PAR's lineage stretches back to the revolutionary praxis of Orlando Fals Borda in South America and Anisur Rahman in Asia. Within psychology, critical PAR is typically linked to the intellectual legacy of Kurt Lewin. In the first section of this chapter, we review a set of equally significant yet shadowed scholars, particularly women, and men of color, who helped carve the scientific path toward critical PAR as practiced within psychology in the 21st century. Each of these scholars invented social psychological methods to contest what Ignacio Martín-Baró (1994) called the "collective lie" of prevailing ideological constructions of social problems and to awaken a sense of injusticethrough research-to mobilize everyday people for change. Our intent in excavating this scholarship is to create an intellectual genealogy for contemporary PAR through a line of critical science projects in which engaged social scientists have collaborated with communities to interrogate the gap between domi...