Hematopoietic stem and progenitor cells from human umbilical cord blood have been the focus of both basic and clinical research during the last 20 years. It has been clearly demonstrated that such sells possess higher proliferation and expansion potentials, as compared to their adult counterparts, and their capacity to reconstitute the hematopoietic system of mammals has also been shown. Different In vitro systems have been used to characterize the biology of these hematopoietic cells and some culture methods are being currently used to expand the numbers of such cells for clinical purposes.