The shoot apical meristem (SAM), which is the tissue located at the top of a plant, can continually undergo differentiation. The SAM gives rise to all aboveground organs, such as the stems, leaves, and flowers, through cell division and differentiation. SAM development is controlled by the external environment, endogenous hormones, and molecular regulation, accordingly with phased characteristics of the SAM. Here, we summarize recent advances in our understanding of the morphological structure of the SAM and how it is affected by environmental factors, hormones, and molecular regulatory networks. We also present the research status on SAM, including unsolved problems and future research directions.