The AK-47 is a selective-fire, gas-operated 7.62x39mm assault rifle, first developed in the Soviet Union by Mikhail Kalashnikov. It is officially known as Avtomat Kalashnikova. It is also known as a Kalashnikov, an "AK", or, in Russian slang, Kalash.

Design work on the AK-47 began in the last year of World War II (1945). After the war in 1946, the AK-46 was presented for official military trials. In 1947 the fixed-stock version was introduced into service with select units of the Soviet Army. An early development of the design was the AKS-47 (SSkladnoy or "folding"), which was equipped with an underfolding metal shoulder stock. In 1949, the AK-47 was officially accepted by the Soviet Armed Forces and used by the majority of the member states of the Warsaw Pact.

The original AK-47 was one of the first true assault rifles. Even after six decades the model and its variants remain the most widely used and popular assault rifles in the world because of its durability, low production cost, and ease of use. It has been manufactured in many countries and has seen service with regular armed forces as well as irregular, revolutionary and terrorist organizations worldwide. The AK-47 was the basis for developing many other types of individual and crew-served firearms. More AK-type rifles have been produced than all other assault rifles combined.

Firing the 7.62x39mm cartridge, the AK-47 produces significant wounding effects when the projectile tumbles and fragments in tissue; but it produces relatively minor wounds when the projectile exits the body before beginning to yaw.

During World War II, the Germans first pioneered the assault rifle concept, based upon research that showed that most firefights happen at close range, within approximately 300 meters. The power and range of contemporary rifle cartridges was excessive for most small arms firefights. As a result, armies sought a cartridge and rifle combining submachine gun features (large-capacity magazine, selective-fire) with an intermediate-power cartridge effective to 300 meters. To reduce manufacturing costs, the 7.92x57mm Mauser cartridge case was shortened, the result of which was the lighter 7.92x33mm Kurz.

 The resultant rifle was the Sturmgewehr 44 (StG44). An earlier firearm, the Italian Cei-Rigotti combined similar features but suffered poor reliability and ejection mechanism, as well as inferior magazine capacity. Towards the end of the war, the Germans fielded the StG44 against the Soviets; the experience deeply influenced Soviet military doctrine in the post-war years.

Mikhail Kalashnikov began his career as a weapon designer while in a hospital after he was shot in the shoulder during the Battle of Bryansk. After tinkering with a sub-machine gun design, he entered a competition for a new weapon that would chamber the 7.62x41mm cartridge developed by Elisarov and Semin in 1943 (the 7.62x41mm cartridge predated the current 7.62x39mm M1943). A particular requirement of the competition was the reliability of the firearm in the muddy, wet, and frozen conditions of the Soviet front line. Kalashnikov designed a carbine, strongly influenced by the American M1 Garand, that lost out to the Simonov design that later became the SKS semi-automatic carbine. At the same time, the Soviet Army was interested in developing a true assault rifle employing a shortened M1943 round. The first such weapon was presented by Sudayev in 1944, but trials found it to be too heavy. A new design competition was held two years later where Kalashnikov and his design team submitted an entry. It was a gas-operated rifle which had a breech-block mechanism similar to his 1944 carbine, and a curved 30-round magazine.

Kalashnikov's rifles (codenamed AK-1 and 2) proved to be reliable and the weapon was accepted to second round of competition along with designs by A.A Demetev and F. Bulkin. In late 1946, as the rifles were being tested, one of Kalashnikov's assistants, Aleksandr Zaytsev, suggested a major redesign of AK-1, particularly to improve reliability. At first, Kalashnikov was reluctant, given that their rifle had already fared better than its competitors. Eventually, however, Zaytsev managed to persuade Kalashnikov. The new rifle was produced for a second round of firing tests and field trials. There, Kalashnikov assault rifle model 1947 proved to be simple and reliable under a wide range of conditions with convenient handling characteristics. In 1949 it was therefore adopted by the Soviet Army as '7.62mm Kalashnikov assault rifle (AK)'.^[12]

The AK-47 is best described as a hybrid of previous rifle technology innovations: the trigger, double locking lugs and unlocking raceway of the M1 Garand/M1 carbine, the safety mechanism of the John Browning designed Remington Model 8 rifle,and the gas system and layout of the Sturmgewehr 44. Kalashnikov's team had access to all of these weapons and had no need to "reinvent the wheel",though he denied that his design was based on the German Sturmgewehr 44 assault rifle. Kalashnikov himself observed: "A lot of [Soviet Army soldiers] ask me how one can become a constructor, and how new weaponry is designed. These are very difficult questions. Each designer seems to have his own paths, his own successes and failures. But one thing is clear: before attempting to create something new, it is vital to have a good appreciation of everything that already exists in this field. I myself have had many experiences confirming this to be so."