Forwarding agents or railroads use freight codes (and sets of freight codes) to classify the goods they transport. Freight codes are specified in the transportation papers, and some are specific to rail or road transportation.

These are compiled in freight code sets published by forwarding agents and the railroad authorities and are used specifically when referring to rail or road transport. Specific freight codes are defined in each freight code set.

Freight classes are made up of one or more freight codes and are one of the criteria for shipment costing.