Polymer-cased ammunition (PCA) is firearm ammunition (cartridge) with casings made from synthetic polymer instead of the typical metallic casing. PCA is commonly seen among shotgun shells, and is considered a new alternative for long guns and handguns that potentially reduces ammunition production cost and weight.

The first references to the possible use of polymers in the manufacture of casings come from the early 1950s. One of the earliest is the patent filed by Jack W. Roske in 1950 and the idea was to use a metal cup joined with a polymer shell "that will be converted to gas during the firing phase to assist in propelling the projectile and thereby permit reduction in the use of the propelling powder charge".