A railway air brake is a railway brake power braking system with compressed air as the operating medium. Modern trains rely upon a fail-safe air brake system that is based upon a design patented by George Westinghouse on April 13, 1869. The Westinghouse Air Brake Company was subsequently organized to manufacture and sell Westinghouse's invention. In various forms, it has been nearly universally adopted.

The Westinghouse system uses air pressure to charge air reservoirs (tanks) on each car. Full air pressure signals each car to release the brakes. A reduction or loss of air pressure signals each car to apply its brakes, using the compressed air in its reservoirs.

George Westinghouse Jr. (October 6, 1846 – March 12, 1914) was an American entrepreneur and engineer based in Pennsylvania who created the railway air brake and was a pioneer of the electrical industry, receiving his first patent at the age of 19. Westinghouse saw the potential of using alternating current for electric power distribution in the early 1880s and put all his resources into developing and marketing it. This put Westinghouse's business in direct competition with Thomas Edison, who marketed direct current for electric power distribution. In 1911 Westinghouse received the American Institute of Electrical Engineers's (AIEE) Edison Medal "For meritorious achievement in connection with the development of the alternating current system."