Paraquat is a toxic chemical that is widely used as an herbicide (plant killer), primarily for weed and grass control.

Paraquat was first produced for commercial purposes in 1961 and is today among the most commonly used herbicides. In the United States, paraquat is available primarily as a liquid in various strengths. It is classified as "restricted use," which means that it can be used only by licensed applicators. Because paraquat is highly poisonous, the form of it that is marketed in the United States has a blue dye to keep it from being confused with beverages such as coffee, a sharp odor to serve as a warning, and an added emetic in case someone drinks it. Paraquat from outside the United States may not have these safeguards added.