Pesticides are designed to kill pests, defined as harmful insects, fungi and weeds. The effects of pesticides on crops and pests are linked to their dose per unit area. The producer usually recommends a dose, which controls the target pests without harming the operator and the crop and without unacceptable pollution of the environment. Although all precautions are taken, pesticides will inevitably affect non-target organisms. A good example is herbicides that are designed to kill plants, but their selective use in crops is a matter of dose. The development and use of pesticides is based upon the use of dose response curves, in just the same way toxicologists and pharmacologists use dose response curves, to classify pesticides in relation to their toxicity on fauna and flora. Consequently, the very same methods used in toxicology and pharmacology can be used in the pesticide sciences.