The fields of sustainability and entrepreneurship share their dynamic processes, their high degree of uncertainty and complexity, and their endeavor on systemic impact. These inherent characteristics call researchers to engage in action research. Action research equips researchers with unique tools to navigate the volatility and complexity of sustainable entrepreneurship while simultaneously fostering its purpose and uncovering new theoretical insights. Yet, action research efforts fostering sustainable entrepreneurship are still emergent, and the mutual affinity between sustainable entrepreneurship and action research is still seldom addressed in the literature and often confused with other forms of collaborative knowledge production and problem-solving such as co-creation and consulting. In this chapter, we discuss the central principles of this form of academic knowledge production, their practices, and implications for sustainable entrepreneurship. We begin by defining action research and its unique methodological features. We then highlight research practices to address two fundamental but overlooked aspects of action research: value reciprocity and impact temporality. We illustrate these aspects by providing two cases of action research in a sustainable entrepreneurship context. This chapter offers directions for the researcher embarking into action research journeys aimed at fostering sustainable entrepreneurship.