.22 LR全名“.22 Long Rifle”，是一历史悠久的底缘底火式（Rimfire）子弹。如以销售记录言，到目前仍然是全世界最普遍的子弹。被使用于许多步枪、手枪、左轮手枪、甚至于滑膛霰弹枪。数十年来是全世界最受欢迎的子弹。也是少数同时被广泛使用于步枪与手枪的子弹之一。超过一世纪以来，几乎每家枪械制造厂最少都会制造一型使用.22 LR的枪械。

廉价，低后座力与噪音小使得.22 LR成为理想的休闲射击用子弹。标准包装每小盒50发，用户通常都购买大盒包装，每大盒内有10小盒500发，或是购买整箱，每箱内有10大盒5000发。每小盒50发在美国2016年的零售价大约$5-$10美元。

The .22 Long Rifle rimfire (metric designation: 5.6×15mmR) 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/-/ˈɑːr/") 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. 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.