In chemistry, a reducing agent or reductant is a substance that transfers electrons to another substance. In other words, it becomes oxidized itself while reducing another substance.

The reductant force is a measure of the tendency of a substance to lose electrons and to reduce other substances. The greater the reductant force, the more likely the substance is to lose electrons and to reduce other substances. The reductant force is determined by the electronegativity of the atoms in the substance. The more electronegative the atoms, the greater the reductant force of the substance.