The .22 Long Rifle rimfire (5.6×15mmR - metric designation) cartridge is a long established variety of ammunition, and in terms of units sold is still by far the most common in the world today. The cartridge is often referred to simply as .22 LR ("twenty-two-/ˈɛl/-/ˈɑr/") and various rifles, pistols, revolvers, and even some smoothbore shotguns have been manufactured in this caliber. The cartridge originated from the Flobert BB Cap of 1845 through the .22 Smith & Wesson cartridge of 1857, and was developed by the American firearms manufacturer J. Stevens Arms & Tool Company in 1887 by combining the casing of the .22 Long with the 40-grain (2.6 g) bullet of the .22 Extra Long. For many decades, it has been a very popular cartridge around the world. It is one of the few cartridges that are accepted by a large variety of rifles, as well as pistols. Virtually every manufacturer of cartridge firearms makes at least one model chambering it, and this has been true for more than a century. The .22 Long Rifle and related cartridges (.22 Short, .22 Long and .22 Extra Long) use a heeled bullet, which means that the bullet is the same diameter as the case, and has a narrower "heel" portion that fits in the case.

Year 22 (XXII) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Agrippa and Galba (or, less frequently, year 775 Ab urbe condita). The denomination 22 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.

The American longrifle, better, but less correctly, known as the Kentucky rifle. It was described by Captain John G. W. Dillin in the dedication to his seminal 1924 book, The Kentucky Rifle:

"From a flat bar of soft iron, hand forged into a gun barrel; laboriously bored and rifled with crude tools; fitted with a stock hewn from a maple tree in the neighboring forest; and supplied with a lock hammered to shape on the anvil; an unknown smith, in a shop long since silent, fashioned a rifle which changed the whole course of world history; made possible the settlement of a continent; and ultimately Freed our country of foreign domination.

Light in weight; graceful in line; economical in consumption of powder and lead; fatally precise; distinctly American; it sprang into immediate popularity; and for a hundred years was a model often slightly varied but never radically changed."

The longrifle developed on the American frontier in and about Lancaster, Pennsylvania in the 1740s.^{[citation needed]} It continued to be developed technically and artistically until it passed out of fashion in the second quarter of the 19th century. Strong pockets of longrifle use and manufacture continued in the Appalachian Mountains of Virginia, Tennessee, Kentucky, and North Carolina, however, well into the 20th century as a practical and efficient firearm for those rural segments of the nation. Longrifles could be made entirely by hand and hand-operated tooling, in a frontier setting.