Hematopoietic stem and progenitor cells (HSPCs) give rise to all blood lineages that support life. HSPCs, like seeds, need a suitable microenvironment to maintain their function. A process called “homing” allows HSPCs to anchor in their niches in order to expand and differentiate. Unique niche microenvironments composed of blood vessels and other niche components, including stromal cells, regulate this process.