In recent years, there has been an increasing interest in non-hematopoietic pluripotent progenitor cells that are found in the bone marrow. Mesenchymal stem cells (MSCs) are the first non-hematopoietic progenitors to be isolated from the bone marrow and extensively characterized. In addition to their ability to support hematopoiesis, MSCs can differentiate into osteocytes, chondrocytes, tenocytes, adipocytes and smooth muscle cells. This article will review our current understanding of bone marrow stroma and MSCs and their potential therapeutic role in the setting of hematopoietic stem cell transplantation.