Seeds which are provided with a suitable temperature, adequate moisture, and oxygen but fail to germinate are called dormant. Certain forms of dormancy in seeds involve certain degree of hormonal control. Gibberellins, cytokinens, inhibitors such as ABA and possibly ethylene, may each be implicated in various species and organs. Studies on the correlation between levels of endogenous hormones and the state of dormancy and observations on the effects of applied exogenous hormones cannot, in themselves establish the role of hormones in the control of dormancy. Although the dormancy of seeds with a chilling requirement quite clearly appears to involve hormonal control, yet their role in other forms of seed dormancy is less convincing. Physical factors arising from the presence of seed coats appear to be the least important. However, even where the coats appear to present an interference with gaseous exchange or a mechanical resistance to germination, possible interactions of such coat effects with hormonal factors cannot be excluded.