Cell therapies for severe ischemic diseases such as limb ischemia, acute myocardial infarction, and cerebral ischemia have been developed through in vitro and in vivo animal and clinical studies. Active cells for angiogenic cell therapy are believed endothelial progenitor cells (EPCs). EPCs have been extensively investigated to clarify their origin and biology. Many sources of EPCs have been proposed, including mononuclear cells (MNCs) fraction containing CD34(+) or CD133(+) (AC133(+)), isolated CD34(+) and AC133(+) cells, and induction and differentiation of EPCs from hematopoietic stem cells (HSCs). However, in vivo mechanisms by which EPCs contribute to neovascularization should be clarified. Many in vitro, in vivo, and clinical studies have been performed using these cells; angiogenic cell therapy will become an important regimen for severe ischemic diseases.