Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. It is used to make most fluorine-containing compounds; examples include the pharmaceutical fluoxetine (Prozac) and the material PTFE (Teflon). Elemental fluorine is produced from it. Solutions of HF are colourless, acidic and highly corrosive. It is in common use to etch glass and silicon wafers.

When hydrofluoric acid comes into contact with human skin it causes deep burns.