Pesticides can be classified by target organism (e.g., herbicides, insecticides, fungicides, rodenticides, and pediculicides – see table),
Biopesticides according to the EPA include microbial pesticides, biochemical pesticides, and plant-incorporated protectants.
Pesticides can be classified into structural classes, with many structural classes developed for each of the target organisms listed in the table. A structural class is usually associated with a single mode of action, whereas a mode of action may encompass more than one structural class.
The pesticidal chemical (active ingredient) is mixed (formulated) with other components to form the product that is sold, and which is applied in various ways. Pesticides in gas form are fumigants.
Pesticides can be classified based upon their mode of action, which indicates the exact biological mechanism which the pesticide disrupts. The modes of action are important for resistance management, and are categorized and administered by the insecticide, herbicide, and fungicide resistance action committees. 
Pesticides may be systemic or non-systemic. A systemic pesticide moves (translocates) inside the plant. Translocation may be upward in the xylem, or downward in the phloem or both. Non-systemic pesticides (contact pesticides) remain on the surface and act though direct contact with target organism. Pesticdes are more effective if they are systemic. Systemicity is a prerequisite for the pesticide to be used as a seed-treatment.
Pesticides can be classified as persistent (non-biodegradable) or non-persistent (biodegradable). A pesticide must be persistent enough to kill or control its target but must degrade fast enough not to accumulate in the environment or the food chain in order to be approved by the authorities. Persistent pesticides, including DDT, were banned years ago, an exception being spraying in houses to combat malaria vectors.