2-bay hopper cars of the Reading Railroad.

A hopper car is a type of railroad freight car used to transport loose bulk commodities such as coal, ore, grain, etc.

This type of car is distinguished from a gondola car in that it has opening doors on the underside or the sides to discharge its cargo. The development of the hopper car went along with the development of more automated handling of such commodities, with automated loading and unloading facilities. There are two main types of hopper car: open or covered.

• Covered hopper cars are used for cargoes that must be protected from the elements, chiefly rain, such as grain, sugar, fertiliser, etc.
• Open cars are used for commodities such as coal which can get wet and dry out with no harm done.

Hopper cars have been used by railways worldwide whenever automated cargo handling has been desired. Recently in North America the open hopper car has been in a terminal decline, because of the rotary car dumper (which simply inverts the car to unload it) which has become the preferred unloading technology. A rotary dumper permits the use of simpler, tougher, more compact (because sloping ends are not required) gondola cars instead of hoppers. Covered hoppers, though, are still in widespread use.