Recent evidence indicates that osteoblasts are crucial components of the particular microenvironments, or niches, for hematopoietic stem cells (HSCs) in adult bone marrow (BM). Stem cells persist in an immature state within the BM. The quiescence of HSCs is controlled dynamically by the signaling of receptors-ligands and cell-adhesion molecules. In this review, the characteristics of HSCs in the niche are discussed. The understanding of the relationship between normal and cancer stem cells and their niches should lead to the development of new strategies directed toward regeneration medicine and cancer therapeutics.