Plants can continuously and repetitively give rise to lateral organs through their meristems. The root apical meristem (RAM) generates the underground parts of plants, whereas the shoot apical meristem (SAM) produces the aboveground parts. The SAM originates from the embryo and gives rise to the aerial parts of plants. Within the SAM, a small number of stem cells confined to the upper region of the central zone (CZ) serve as the ultimate source of all shoot cells. Shoot stem cells have a strong ability to renew themselves and to generate daughter cells to produce new tissues. The plasticity of shoot stem cells allows plants to adapt their shape in response to developmental, physical, and environmental cues. The balance between the proliferation and differentiation of stem cells determines their populations in the SAM. The elaborate genetic network that regulates the initiation and maintenance of shoot stem cells has been a major area of interest in plant developmental research for decades.