Binary Chemical Weapons are chemical weapons wherein the toxic agent is not contained within the weapon in its active state, but in the form of two chemical precursors, physically separated within the weapon. The precursors are designed to be signifcantly less toxic than the agent they make when mixed, and this allows the weapon to be transported and stored more safely than otherwise. When the weapon is released, the precursors are allowed to mix.

One example of a binary chemical weapon is the United States Army M687. In the M687, methylphosphonyl difluoride and a mixture of isopropyl alcohol and isopropyl amine are held in chambers within the weapon, separated by a partition. When the weapon is fired, acceleration causes the partition to break, and the precursors are mixed by the rotation of the weapon in flight, producing sarin nerve gas.