The FN Four was the world's first production inline-4 motorcycle, manufactured in Liége[4] by Fabrique Nationale from 1905 until 1923.

[13] The 1905 model had a high-tension Bosch magneto ignition,[14]: 43  a spray carburetor, and a rear coaster brake operated by the pedals.

[15] Engine power was raised from 4+1⁄2 hp (3.4 kW) to 5 hp (3.7 kW), the frame size was reduced from 22 to 20 inches (560 to 510 mm) allowing the rider to sit with both feet on the ground, the wheel rims were made heavier and would fit American tire sizes, and it came with tires with a heavier tread.

[14]: 43  The US model had either Goodrich or another imported brand of tires, and a leather seat made by the Mesinger Bicycle Saddle Company of New York.

It was preceded by a boxer 4 manufactured in 1897 by Henry Capel Lofft Holden,[19][20] and an obscure air-cooled inline-four developed in 1903 by C. Binks of Nottingham, England, but never produced commercially.

[5] Pierce-Arrow's Percy Pierce brought a 1908 FN Four home from Europe to disassemble and study.

[9] In 1908 another FN Four took the gold medal in a Motor Cycling Club endurance race on the 1,400-kilometre (870 mi) London–Edinburgh–London course.

Models are in the permanent collections of Petersen Automotive Museum in Los Angeles,[32] Seal Cove Auto Museum in Seal Cove, Maine,[33] the Musée de la moto et du vélo in Amnéville France,[34] and others.