Stem cells are not only units of biological organization,responsible for the development and the regeneration oftissue and organ systems, but also are units in evolution bynatural selection. It is accepted that there is stem cellpotential in the liver. Like most organs in a healthy adult,the liver maintains a perfect balance between cell gain andloss. It has three levels of cells that can respond to loss ofhepatocytes: (1) Mature hepatocytes, which proliferate aftormal liver tissue renewal, less severe liver damage, etc;they are numerous, unipotent, committed and respondrapidly to liver injury. (2) Oval cells, which are activated toproliferate when the liver damage is extensive and chronic,or if proliferation of hepatocytes is inhibited; they lie withinor immediately adjacent tothe canal of Hering (CoH); theyare less numerous, bipotent and respond by longer, but stilllimited proliferation. (3) Exogenous liver stem cells, whichmay derive from circulating hematopoietic stem cells (HSCs)or bone marrow stem cells; they respond to allyl alcoholinjury or hepatocarcinogenesis; they are multipotent, rare,but have a very long proliferation potential. They make amore significant contribution to regeneration, and evencompletely restore normal function in a murine model ofhereditary tyrosinaemia. How these three stem cellpopulations integrate to achieve a homeostatic balanceremains enigmatic. This review focuses on the location,activation, markers of the three candidates of liver stemcell, and the most importantly, therapeutic potential ofhepatic stem cells.