This book is written by experts in the field of hematopoietic stem cell biology and lymphocyte development in order to overview recent advances in the field. Prospective isolation of various progenitors and stem cells enables us to understand self-renewal mechanisms of stem cells as well as regulation of hematopoiesis. Furthermore, the importance of extrinsic factors has been emphasized recently. This volume concisely describes our current understanding of normal hemato/lymphopoiesis as well as abnormal hematopoiesis, which may lead to leukemia.