The .375 Weatherby Magnum (9.5×73mmB) is a medium-bore rifle cartridge. The cartridge is blown out, improved and provided with the Weatherby double radius shoulder – given the Weatherby treatment – version of the .375 H&H Magnum. Unlike other improved versions of the .375 H&H Magnum like the .375 Ackley Improved, the .375 Weatherby Magnum is not a wildcat and existed as a proprietary cartridge until the CIP published specifications for the cartridge.

Weatherby, Inc. is an American gun manufacturer founded in 1945 by Roy Weatherby. The company is best known for its high-powered magnum cartridges, such as the .257 Weatherby Magnum, .270 Weatherby Magnum, .300 Weatherby Magnum, .340 Weatherby Magnum and the .460 Weatherby Magnum. The company's headquarters is in Sheridan, Wyoming.