This cluster of papers focuses on the biology, regulation, and clinical applications of hematopoietic stem cells (HSCs) within the bone marrow niche. It covers topics such as HSC quiescence, stem cell aging, graft-versus-host disease, hematologic malignancies, and the role of mesenchymal stem cells in supporting HSC function. Additionally, it explores the mechanisms of stem cell mobilization and transplantation for therapeutic purposes.