Technical Abstract: Plant development, or the progression of plants through their life cycle, has been of great interest in human history because of the need to know and predict when the harvested part of the plant was at the optimum stage. This knowledge was especially important (even vital) in medicinal plants, where the timing of harvesting defines the medicinal value of the product. This interest increased as groups moved from hunting and gathering to agrarian societies. Crop development can be defined with the number and rate of appearance, growth and senescence of phytomers. However, that definition lacks information about when the switch of vegetative to reproductive phytomers occurs, which is defined by the phenology of the crop. Crop development is of great importance in agriculture because it is the main mechanism plants use to escape both biotic and abiotic stresses, and adapt to the environment. At a more practical level, it affects the management of the crop because cultural practices are more effective at specific stages of crop development. This paper discusses crop development and phenology with the emphasis on temperate cereals.