The 1939–40 New York World's Fair was a world's fair held at Flushing Meadows–Corona Park in Queens, New York, United States. It was the second-most expensive American world's fair of all time, exceeded only by St. Louis's Louisiana Purchase Exposition of 1904. Many countries around the world participated in it, and over 44 million people attended its exhibits in two seasons. It was the first exposition to be based on the future, with an opening slogan of "Dawn of a New Day", and it allowed all visitors to take a look at "the world of tomorrow".

When World War II began four months into the 1939 World's Fair, many exhibits were affected, especially those on display in the pavilions of countries under Axis occupation. After the close of the fair in 1940, many exhibits were demolished or removed, though some buildings were retained for the 1964–1965 New York World's Fair, held at the same site.