Cytokinins are a major group of plant hormones that control various processes in plant growth and development. Chemically they are N6-substituated adenine derivatives, including their respective ribotides, ribosides and glucosides. The inter-conversion between different cytokinins metabolites represents the transition between active, inactive, storage and transport forms. This process is in vivo rather dynamic and rapid. We have finally begun to understand the role of cytokinins in plant development through the identification of genes for the first plant enzyme in the biosynthetic pathway, isopentenyl transferases, less than 10 years ago, in addition to research of other enzymes and their corresponding genes that are involved in cytokinin metabolism and signal transduction. This review focuses on the recent findings on cytokinins with an emphasis on their role during the development of seedsfrom which the first natural cytokinin was isolated more that half a century ago.