The Royal Enfield Bullet is an overhead valve, single-cylinder, four-stroke motorcycle initially made by Royal Enfield in Redditch, Worcestershire England. It is now produced by Royal Enfield at Chennai, Tamil Nadu, India, a company originally founded by Madras Motors to build Royal Enfield motorcycles under licence in India. The Royal Enfield Bullet has the longest and unchanged production run of any motorcycle having remained continuously in production since 1932. The Bullet marque is even older and has passed 75 years of continuous production. The Royal Enfield and Bullet names were derived from the British company which had been a subcontractor to the Royal Small Arms Factory in Enfield, London.

The Bullet has evolved from a four-stroke engine with exposed valve-gear to the latest all-alloy unit construction engine with electronic fuel-injection.

Introduced in 1932 as a four-stroke single-cylinder motorcycle, this model was the first to feature the Bullet name. It was different in a number of ways from its successors (which are now familiar): it had an inclined engine with exposed valve gear featuring four valves per cylinder with 350 cc and 500 cc options. In 1933, a 250 cc option was also added to the range. Its frame was also considerably different, having centre-spring girder front forks, being among a new range of models from Royal Enfield that featured them, along with a saddle-type fuel tank. However, common to motorcycles of this period, it had a rigid rear-end, necessitating a 'sprung' seat for the rider, which resulted in the iconic look of the motorcycle that is much replicated today, even though the sprung seat is unnecessary in modern models.

After competition success the 350 cc Royal Enfield Bullet was bought by the British Army for dispatch riders and 3,000 were also supplied to the RAF during the Second World War.

This model refreshed Royal Enfield's model line-up for 1939. It differed in cosmetic details, as well as in having two rocker boxes, which resulted in higher volumetric efficiency for the engine. The post-war models incorporated a hydraulic front fork, and Enfield were among the first among British bikes to develop a fully incorporated swing-arm frame rear suspension. The "bullet" engine also used an aluminium cylinder head.

A number of changes were implemented in order to bring the bike up to date. This model featured a vertical engine with an alloy head and higher compression. The frame was changed to a fully sprung design using a swing arm with non-adjustable hydraulic shockers at the rear, while the front used a brand-new telescopic fork of Royal Enfield's own design. This enabled the introduction of a dual seat made of simple foam with no large springs. Power transmission was via the same four-speed Albion gearbox as the previous model, with a unique 'neutral-finder' lever the rider could press from any gear other than first to shift to neutral. The crankshaft continued to have a fully floating big-end bearing. The headlight assembly was enclosed with the speedometer and ammeter into a nacelle, which also served as the attachment of the front suspension as well as the handlebars. An otherwise similar model, but with an engine displacement of 499 cc, made its debut in 1953.

The prototype had done well in a performance trial and went on to win the trophy at the 1948 International Six Days Trial, two Bullet riders won gold medals. In 1952 Johnny Brittain won the Scottish Six Days Trial on a Royal Enfield Bullet and in 1953 he also won the International Six Days Trial without losing a single point.

In 1949, the Indian Army ordered Royal Enfield Bullets for border patrol use and the company decided to open a factory in Madras. In 1955, the 350 cc Bullets were sent from the Redditch factory in kit form for assembly in India, but Enfield India Ltd. soon developed the factory and produced complete motorcycles independently under licence. The 1955 model remained almost unchanged for years and Madras produced over 20,000 Bullets annually.