The liver is a central organ for homeostasis with unique regenerative capacities. Mature hepatocytes possess a remarkable capacity to proliferate upon injury, challenging efforts to discern the role of adult liver stem cells in this process. In contrast, stem/progenitor cells in the developing liver have been extensively characterized, and these investigations have informed efforts to produce functional hepatocytes in vitro for cell therapy and drug screening. In this Review, we describe recent advances in the characterization of liver stem cells and discuss evidence supporting and refuting whether self-renewable and bipotential liver stem cells exist in development, homeostasis, regeneration, and disease.