Employment precariousness is a social determinant that affects the health of workers, families, and communities. Its recent popularity has been spearheaded by three main developments: the surge in “flexible employment” and its associated erosion of workers’ employment and working conditions since the mid-1970s; the growing interest in social determinants of health, including employment conditions; and the availability of new data and information systems. This article identifies the historical, economic, and political factors that link precarious employment to health and health equity; reviews concepts, models, instruments, and findings on precarious employment and health inequalities; summarizes the strengths and weaknesses of this literature; and highlights substantive and methodological challenges that need to be addressed. We identify two crucial future aims: to provide a compelling research program that expands our understanding of employment precariousness and to develop and evaluate policy programs that effectively put an end to its health-related impacts.