A ballistic knife is an automatic knife with a detachable blade that can be expelled from the handle/frame as a projectile by means of a spring-operated or gas-driven mechanism.

Ballistic knives, manufactured by the USSR company Ostblock, were supplied in large numbers to the Soviet special forces group Spetsnaz. Unlicensed copies of these knives appeared in the US in the early 1980's.

Ballistic knives were designed to be used as covert weapons when a firearm is not appropriate. The blade can remain attached to the handle and used as a typical fixed-blade knife or launched as a projectile by pulling a pin and pressing a button. The spring in these knives is powerful enough to propel the blade to about 6 metres (about 18 feet) or more at 63 km/h (39 mph).