Alongside the growing interest within HCI, and arguably computing more generally, in conducting research that has substantial societal benefits, there is a need for new ways to think about and to articulate the challenges of these engaged research projects as well as their results. Action Research (AR) is a class of methods and approaches for conducting democratic and collaborative research with community partners. AR has evolved over the last several decades and offers HCI researchers theoretical lenses, methodological approaches, and pragmatic guidance for conducting socially relevant, collaborative, and engaged research. In this article, I describe the historical context and origins of AR, the scientifically rigorous practice of conducting and evaluating AR projects, and the ways in which AR might meaningfully be applied to HCI research.