Boric acid, also called hydrogen borate and boracic acid, is a weak, monobasic Lewis acid of boron, which is often used as an antiseptic, insecticide, flame retardant, neutron absorber, or precursor to other chemical compounds. It has the chemical formula H3BO3 and exists in the form of white powder that dissolves in water.

Boric acid has been used to control a wide variety of pests. It has also been used as a fungicide for citrus, a herbicide along rights-of-way, a fire retardant and a wood preservative. When used as a herbicide, it causes desiccation and disrupts photosynthesis in plants.

Boric acid is also used in industry, with its main use being in the manufacturing of textile fibreglass. It is used to reinforce plastics in various products, such as boats, computer circuit boards and pipes.