Cytokinins are master regulators of plant growth and development. They are involved in the regulation in many important physiological and metabolism processes. It is always the most important topic to investigate the cytokinin actions in plant science. In this review, we briefly introduce the discovery and research history of cytokinins. Particularly, the recent progress in cytokinin at the molecular level is discussed, which includes biosynthetic route, related gene identification, receptors and signal transduction, and transgenic plants. Based on the information generated to date, implications and future research directions are presented.