In vascular development, uncommitted cells differentiate into different xylem cells through vascular stem cells, such as procambial cells, during vein formation as well as embryogenesis. Cascades of transcriptional regulation of genes play crucial roles in the progress of vascular development. Auxin, cytokinin, and brassinosteroids also function in procambial cell determination, procambial maintenance, and xylem cell differentiation from procambial cells, respectively, through transcriptional regulation. The positive feedback loop typically shown in auxin-flow-MONOPTEROS-(HD-ZIP IIIs)-PIN1-auxin-flow in procambial precursor cell determination and VND7-ASL/LBD-VND7 in xylem vessel cell determination, may be a crucial mechanism that determines vascular cell fates, which occurs in stages.