There are four main types of air cargo carriers that provide different services: 1) Integrated express operators like FedEx, UPS, and DHL that offer door-to-door delivery using aircraft and trucks; 2) All-cargo carriers like Atlas Air Cargo that operate scheduled flights between major airports; 3) Commercial passenger airlines like Delta and Lufthansa that carry cargo in the bellies of passenger planes; 4) Ad-hoc charter carriers like Grand Aire that provide unscheduled airport-to-airport cargo flights. These carriers offer three primary service types: integrated express service, freight forwarding, and airport-to-airport service.