The term Link Trainer, also known as the "Blue box" and "Pilot Trainer", is commonly used to refer to a series of flight simulators produced between the early 1930s and early 1950s by Link Aviation Devices, founded and headed by Ed Link, based on technology he pioneered in 1929 at his family's business in Binghamton, New York. During World War II, they were used as a key pilot training aid by almost every combatant nation.

The original Link Trainer was created in 1929 out of the need for a safe way to teach new pilots how to fly by instruments. Ed Link used his knowledge of pumps, valves and bellows gained at his father's Link Piano and Organ Company to create a flight simulator that responded to the pilot's controls and gave an accurate reading on the included instruments. More than 500,000 US pilots were trained on Link simulators, as were pilots of nations as diverse as Australia, Canada, Germany, New Zealand, United Kingdom, Israel, Japan, Pakistan, and the USSR. Following WWII, Air Marshal Robert Leckie (wartime RAF Chief of Staff) said "The Luftwaffe met its Waterloo on all the training fields of the free world where there was a battery of Link Trainers".

The Link Flight Trainer has been designated as a Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers. The Link Company, now the Link Simulation & Training division of CAE USA Defense & Security CAE Inc., continues to make aerospace simulators.

Edwin Link had developed a passion for flying in his boyhood years, but was not able to afford the high cost of flying lessons. So, upon leaving school in 1927, he started developing a simulator. The project took him 18 months. His first pilot trainer, which debuted in 1929, resembled an overgrown toy airplane from the outside, with short wooden wings and fuselage mounted on a universal joint. Organ bellows from the Link organ factory, the business his family owned and operated in Binghamton, New York, driven by an electric pump, made the trainer pitch and roll as the pilot worked the controls.

Link's first military sales came as a result of the Air Mail scandal, when the Army Air Corps took over carriage of U.S. Air Mail. Twelve pilots were killed in a 78-day period due to their unfamiliarity with Instrument Flying Conditions. The large scale loss of life prompted the Air Corps to look at a number of solutions, including Link's pilot trainer. The Air Corps was given a stark demonstration of the potential of instrument training when, in 1934, Link flew in to a meeting in conditions of fog that the Air Corps evaluation team regarded as unflyable. As a result, the Air Corps ordered the first six pilot trainers on 23 June 1934 for $3,500 each. In 1936, the more advanced Model C was introduced.

American Airlines became the first commercial airline to purchase a Link trainer in 1937. Prior to World War II, Link trainers were also sold to the U.S. Navy, Civil Aeronautics Administration, Germany, Japan, England, Russia, France, and Canada.

Link and his company had struggled through the Depression years, but after gaining Air Corps interest the business expanded rapidly and during World War II, the AN-T-18 Basic Instrument Trainer, known to tens of thousands of fledgling pilots as the "Blue Box" (although it was painted in different colors in other countries), was standard equipment at every air training school in the United States and Allied nations. During the war years, Link produced over 10,000 Blue Boxes, turning one out every 45 minutes.

During World War II, Link trainers were sometimes run by women.