The shoot apical meristem (SAM) is a reservoir of stem cells that gives rise to all post-embryonic above-ground plant organs. The size of the SAM remains stable over time owing to a precise balance of stem cell replenishment versus cell incorporation into organ primordia. The WUSCHEL (WUS)/CLAVATA (CLV) negative feedback loop is central to SAM size regulation. Its correct function depends on accurate spatial expression of and A signaling pathway, consisting of ERECTA family (ERf) receptors and EPIDERMAL PATTERNING FACTOR LIKE (EPFL) ligands, restricts SAM width and promotes leaf initiation. Although ERf receptors are expressed throughout the SAM, EPFL ligands are expressed in its periphery. Our genetic analysis of demonstrated that ERfs and CLV3 synergistically regulate the size of the SAM, and is epistatic to ERf genes. Furthermore, activation of ERf signaling with exogenous EPFLs resulted in a rapid decrease of and expression. ERf-EPFL signaling inhibits expression of and in the periphery of the SAM, confining them to the center. These findings establish the molecular mechanism for stem cell positioning along the radial axis.