Seeds are the prime source of food in the world, not only from a nutritional point of view but also as the basis of crop production. A key requirement for farmers is vigorous and fast-germinating seed to guarantee a uniform crop of high yield. This is quite opposite to the natural behaviour of seeds which employ dormancy to spread the risk of premature death over time. This chapter addresses the genetic and molecular mechanisms of dormancy and germination. It highlights some of the most important regulatory principles, particularly in relation to the inherent complexity of the seed as a biological system, entailing numerous layers of organisation and regulation, from cells to the environment.