The first comprehensive review of the occurrence and explanation of seed dormancy in grasses is presented in this volume. An understanding of seed dormancy is of considerable significance to world agriculture and the global economy, since grasses are a principal source of food for humankind and play an essential role in stabilizing the land surface of much of the globe. Experimental evidence is considered in depth for a single species, the wild oat (Avena fatua), probably the most widely studied species for understanding seed dormancy in the plant kingdom. The evidence for this species is compared with other examples among the Gramineae to reach some general conclusions about the nature of seed dormancy in grasses.