Technical Abstract: Initiation of seed germination is a critical decision for plants. It is important for seed populations under natural conditions to spread the timing of germination of individual seeds to maximize the probability of species survival. Therefore, seeds have evolved the multiple layers of mechanisms that repress or delay germination including dormancy. Physicochemical properties of seed covering tissues such as testa and endosperm affect the occurrence or the timing of seed germination. Physiological repression may be present in the embryo itself in some species. Plant hormones such as abscisic acid and gibberellin affect the physiological status of the embryo. The repression imposed by abscisic acid can be overcome by gibberellin or other environmental factors such as light and cold temperature. Gibberellin can also affect abscisic acid levels in seeds. Understanding the mechanisms of repression and de-repression in seeds is crucial for the development of new biotechnology to improve seed performance.