Glocks are fairly new to the gun scene.  They first showed up in the in the 1980's and became popular among law enforcement.  They are still in use by many government agencies.  They are boast simplicity, reliability, and value.  They are modestly priced with a retail sticker around $600 for base models.

They are very popular among civilians for self defense and concealed carry.  Glocks have a very simple design which is often criticized because they do not have a manual safety.  Glocks are designed with the safety built into the trigger.  It is designed to discharge only when pulled naturally.

Glocks are produced in various models based on size and caliber.  The most popular model is the Glock 19 which is a compact 9mm.  The model number does not seem to have any rhyme or relation to the size or caliber. 

Popular Models:

Glock 21 = full size .45 ACP
Glock 22 = full size .40 S&W
Glock 17 = full size 9mm

Glock 38 = compact .45 ACP
Glock 23 = compact .40 S&W
Glock 19 = compact 9mm

Glock 30 = subcompact .45 ACP
Glock 27 = subcompact .40 S&W
Glock 26 = subcompact 9mm

Other models are produced in 10mm, .380, .357, and the Glock proprietary .45 GAP.  Certain models are marked with a C at the end.  For example, a Glock 21C is a standard Glock 21 with a ported barrel and slide which aids in reducing recoil and thereby making the weapon easier to shoot.  Glocks are great firearms with tons of accessories.  The magazines are fairly cheap and several other firearms are designed to use Glock magazines.

Generations

At the time of this article Glock's most current model is generation 4.  Previous versions being older and every generation has brought some much needed improvement over previous generations.  Generation 1 models are often sought after by collectors.

Generation 4 guns have gone through some controversy regarding their reliability.  I personally picked up Glock 19gen4 and experienced the same problems as many others.  Various reliability issues were present with 9mm models.  Glock eventually "voluntarily" issued replacement recoil springs to fix the problem. I have personally seen and heard requests for Generation 3 over Generation 4. After breaking in my generation 4 I have had no problems with it.