Wheellock, also referred to as 'Wheel-Lock', was the next major development in firearms technology after the matchlock. It is named for its mechanism, which used a spring and wheel to provide ignition. It was the first self-igniting firearm. Developed in the early 16th century, it was used along-side the matchlock and was later superseded by the snaphance (1580s) and the flintlock (c. 1600).

The design of the wheellock is comparable to that of a modern-day cigarette lighter. A serrated, spring-loaded metal wheel was pressed against a sparking material, usually a small piece of iron pyrite, which was held firm in a cock. When the trigger was pulled, the tightly-wound wheel was released and would spin rapidly, scraping against the pyrite. This generated sparks that fell into the priming pan, igniting its powder and then the main charge. Each firing of the gun required the main spring to be rewound using a special lever. This was called 'spanning the lock'. The sparking material would usually give about a dozen shots before it needed replacing. The wheellock took around a minute to load, prepare and fire.

The wheellock's invention is usually credited to the German Johann Kiefuss in 1517. However, it is unlikely he was the actual inventor. His is the first name to be linked to the gun. There's a possibility that Leonardo da Vinci was the inventor. There are actual drawings made by da Vinci of a wheellock mechanism dating from the first decade of the 1500s.

Among the advantages of the wheellock was a comparatively better resistance to rain or damp conditions: sparks could be generated in any weather, and the priming pan was fitted with a cover that was not raised until the instant the gun was fired. Still, the high production cost hindered the gun's widespread adoption. A highly skilled gunsmith was required to build the complex mechanism, and it was this complexity that was the mechanism's chief disadvantage. The variety of parts and complex design of the wheellock made it liable to break and/or jam. It was also difficult to keep clean, maintain, and repair. Early designs also had trouble creating reliable springs, though this problem was solved in time.

The wheellock was used along with the matchlock until both were replaced by the faster, simpler, and less costly flintlock of the 1600s. However, the ability of the wheellock to fire reliably in wet conditions meant that well-made guns of this design would continue to see use until the 18th century.

The term Wheellock also refers to American inventor Thomas P. Wheellock . Thomas Wheellock and Ethan Allen produced a single-action revolver in the United States during the mid-1800s. The 'Allen and Wheellock' revolver was reloaded by removing the whole cylinder after unloosening a screw. This resulted in long reload time but reduced production cost due to the simplicity of the design. It was generally bought as a pocket pistol for occasional use.