Harley-Davidson motorcycles were manufactured in Milwaukee, Wisconsin, from 1903 through 1972. Since 1972 all f the motorcycles have been built in Milwaukee and shipped to Pennsylvania. In 1901 William Harley and Arthur Davidson started experiments on "taking the work out of bicycling." The first productions began in a shed behind the Davidson family home. Only 3 Harley-Davidsons were made in 1903 (25 cubic inch-410cc-atmospheric-inlet-valve single-cylinder).

The company was founded in 1903. It finally became incorporated in 1907. In 1907 only 150 motorcycles were made, but 1907 was also the year when Harley-Davidsons were sold for police duty. The first Harley sold with a clutch was in 1912. Stepstarters and internal expanding rear brakes were introduced in 1914.

When the U.S. entered World War I some 20,000 cycles were used for transportation. In 1920 Harley-Davidson became the largest motorcycle manufacturer in the world. The safety and handling of Harley-Davidson's cycles were improved in 1928 with front wheel brakes. In 1933 Harley-Davidson was hit hard by the Depression, production dropped to 3,700 vehicles. Many people say that the first "Knucklehead" (1936) was the motorcycle that saved Harley-Davidson. After Pearl Harbor, Harley-Davidson's entire output was produced for allied use.

In 1942 Walter Davidson died at the age of 65. One year later, Bill (William) Harley died at the age of 66. Arthur Davidson died in 1950 at the age of 69. Harley-Davidson celebrated its 50th Anniversary and produced 14,050 motorcycles.

Harley-Davidson bought the Italian Aermacchi company. The Italian-lightweights were sold in America under the Harley-Davidson name. The shortster and sprint models are some examples. In 1963 Harley-Davidson purchased a fiberglass company because it became apparent that fiberglass was versatile for golf cars and motorcycles. In 1965 Harley-Davidson became a publicly-held company when it issued stock.

In 1969 Harley-Davidson took a new turn by merging with the American Machine and Foundry Co. From 1974 through 1975 Harley-Davidson operations were moved to a plant in York, Pennsylvania. Engine and transmission operation stayed in Milwaukee. In 1978 Harley-Davidson sold the Italian operation (Aermacchi) and the sales of Italian motorcycles. Harley-Davidson exectives bought the company back from AMF and developed new models and new images in 1981. Also in 1981 many of the old flaws of the H-D design were resolved because the manufacturing and quality process was improved.