The chapter introduces various terms applied to chemicals that are used to control agricultural pests. The limited crop protection methods ancient farmers employed to save crops from weeds, and other invading pests included treatment with various materials of dubious efficacy. As new knowledge gathered during and after the Renaissance, people started to understand the etiology of the outbreaks and develop effective control measures. The twentieth century saw the discovery of highly efficacious modern agrochemicals, which were rapidly adopted by the farming community due to a great reduction in efforts and savings in costs. Prominent groups of herbicides, insecticides, and fungicides classified according to their modes of actions are presented to show the structural varieties and functional ranges of these agrochemicals. The regulation of pesticides through enactment of laws to protect human life and the environment from perceived harmful effects of agrochemicals is discussed in detail. The chapter also presents how the EPA and other regulatory agencies around the world administer the agrochemical registration process, what type of scientific data are required, and how the quality of data is maintained through compliance with good laboratory practice standards. The agencies evaluate these data to safeguard people and the environment from any unreasonable risk arising from the use of the agrochemical product.