First introduced to the market in 1985, there are now more than 170 variations of the Glock pistol when all of the generations, calibers, and sizes are involved, and here is an easy breakdown on how to tell them apart.
Developed from a clean sheet design by Herr Gaston Glock in Austria in the late 1970s/early 1980s to compete for an Austrian Army contract for a new sidearm, his polymer-framed 9mm pistol was innovative, famously using just 33 parts but clocking in with an impressive 17+1 magazine capacity. Long story short, his new pistol was adopted by the Austrians as the P80, and a commercial version, the G17, soon hit the market.
The first articles on the new polymer-framed parabellum started popping up in Sept. 1985 (See Plastic Packs a Punch, American Handgunner) followed by ads for the guns themselves early the next year.
This standard "full-sized" Glock evolved over the past four decades to include a select-fire version (the G18), as well as variants chambered in .40 S&W (the G22), 10mm Auto (G20), .45 ACP (G21), .357 SIG (G31) and .45 GAP (G37). Across the larger calibers, the magazine capacity dropped and the weight picked up to the point that a G21 has a 13+1 .45 ACP capacity at 29.28-ounces empty, compared with the G17's 17+1 9mm capacity at 24.87-ounces, but that is to be expected.
In 1988, a slightly scaled-down variant of the G17 was introduced which had a 4.02-inch barrel-- down from the G17s 4.49-inches-- while the grip was similarly cut down about a half-inch. This resulted in a still very effective pistol, the G19, that proved to be easier to carry while retaining a 15+1 magazine capacity.
Partially as a side-effect of the 1994 Federal Assault Weapon Ban, which put the kibosh on magazines capable of holding more than 10 cartridges, Glock introduced the G26. The subcompact 9mm used a 3.43-inch barrel-- about half an inch shorter than the G19-- but stood only 4.17-inches high due to its 10+1 magazine capacity, nearly an inch shorter. While still a big blocky for pocket carry, the G26 still compared in size favorably to the classic snub-nosed revolver and brought both higher capacity and faster reload.
Soon after the G17 was introduced, Glock moved to fill a demand for a more target-oriented model which yielded the G17L in 1988. This model stretched the top half of the standard full-sized 9mm pistol to produce a 6.02-inch barrel. Coupled with a better trigger, the G17L was soon punching paper in clubs across the country, its longer sight radius aiding in accuracy.
The sauce was applied to other variants in larger calibers to produce the G24 (.40 S&W), and G40 (10mm). In the same vein, Glock introduced practical/tactical models geared to be at home both in the hands of competition shooters and specialty users. This included the G34 (9mm), the G35 (.40 S&W), and G41 (.45 ACP).
With Glock's original .380 ACP models-- the G25 and G28-- largely unobtanium on the commercial market in the U.S., the company introduced the American-made G42 in 2013. With a 13.76-ounce unloaded weight, it is the company's lightest handgun, tipping the scales at even less than the .22LR-caliber G44. This is primarily due to its short 5.94-inch overall length and a single-stack mag with a 6+1 capacity.
In true Glock fashion, the company repeated the G42's success with the follow-on G43 (9mm). The often-forgotten G36, Glock's first single-stack, is in .45 ACP but runs closer in size to the Baby Glock series.
Blurring the lines between the models are Glock's "Crossover" models which blend elements of previous pistols to produce something different. This was first seen on a production gun when the G19X was debuted in 2017. The G19X combined the grip module of the G17 with the shorter top half of the G19 and is produced in Coyote Tan, another Glock first.
In a continuation of this story, the Glock 43X and very similar G48 used a taller grip module, similar in size to the G19, which gave it a 10+1 capacity in 9mm. The 9mm G45, introduced in 2018, dropped the "X" from its designation but is also a crossover, using a compact slide on a full-sized frame.