Methylphosphonyl difluoride (DF), also called methyl difluorophosphite, methylphosphonic difluoride, and difluoromethylphosphine oxide, is a chemical weapon Precursor. It is a Schedule 1 substance in the sense of the Chemical Weapons Convention. It is used for production of sarin and soman. Its chemical formula is CH₃POF₂.

Methylphosphonyl difluoride can be used as a component of binary chemical weapons; an example is the M687 artillery shell, where it is used together with a mixture of isopropyl alcohol and isopropyl amine, producing sarin.