Paris Gun, any of several long-range cannon produced by the German arms manufacturer Krupp in 1917–18 during World War I. The guns were so called because they were specially built to shell Paris at a range, never before attained, of approximately 121 km (75 miles).

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The guns were fabricated by adding a tube to the barrel of a 380-millimetre naval gun. The barrel was thus elongated to about 34 m (112 feet), weighed 138 tons, and needed supports to hold it straight. A charge of 250 kg (550 pounds) of gunpowder was used to propel a shell out of the barrel at a velocity of 5,260 feet per second. The extremely long range of the guns (35 km had been the previous range limit for shellfire) was achieved by sending the shells on a trajectory 39 km (24 miles) up into the stratosphere, where atmospheric drag was almost nonexistent. After modifications, the Paris Guns were initially 210 mm (8.2 inches) in calibre, but successive firings eroded the inner linings of the gun barrels and their calibre was increased to about 240 mm. The Paris Guns were moved to their emplacements near the German front lines on railway tracks and successively carried out an intermittent bombardment of Paris over a period of about 140 days, beginning in March 1918.

The Paris Guns killed about 250 Parisians and wrecked a number of buildings, but they did not appreciably affect French civilian morale or the larger course of the war. The name Big Bertha, which was derisively applied to the guns by Parisians under bombardment from them, is more properly applied to the 420-millimetre howitzers used by the German army to batter Belgian forts in August 1914, at the start of the war.