The 9mm Parabellum
Aka: 9x19, 9mm Luger, 9mm NATO, and just "9mm"

The 9mm Parabellum is one of our oldest autopistol cartridges and it just keeps getting better all the time.  Introduced in 1902 it is even more popular today than it has ever been. There are quite a few other 9mm cartridges, but when you hear someone say "9mm" this is the one they usually mean. It was developed specifically as a military cartridge, hence the name "Parabellum" from the Latin phrase "
Si vis pacem, para bellum
" -- a Latin phrase meaning "If you wish for peace, prepare for war"

The 9mm Parabellum is the single most popular military handgun cartridge in the world. Nearly every nation's military uses or has used it with the exception of the former Warsaw Pact countries who eschewed using any cartridge that was common to the NATO alliance.

In the 1960s and before, the 9mm Parabellum was pooh-poohed as not having enough "stopping power" for military, police, and self-defense use. This was mainly due to the overwhelming use of round-nose full-metal jacketed bullets at that time. The introduction of reliable Jacketed Hollow Point (JHP) bullets changed that forever. True effective "stopping power" from a handgun round remains elusive. Human beings are very hard to stop when they are determined. Police dapartments across the USA switched to the 9mm in the 1980s giving up their six-shot revolvers to have nearly the same amount of power and more than twice the number of rounds on tap. Then, after the 1986 Miami shootout, the search for a more powerful pistol round was begun in earnest, with the FBI leading the way. The eventual result was the overwhelming adoption of the .40 S&W cartridge by American police departments. Today, in mid-2015, many police departments are returning to 9mm handguns citing the belief that no one round is powerful enough to stop a determined attacker with only one hit. The current thinking is that in any police shooting scenario multiple hits will be needed and even more shots will have to be fired. The extra magazine capacity of the 9mm Parabellum round compared to wider rounds like the .40 S&W, 10mm, or the .45 ACP is seen as more important than the fatter rounds' greater power. I suppose time will tell.

As a military cartridge the 9mm has the same advantage of high magazine capacity and no soldier ever said: "Wow. I wish I had taken less ammo into that firefight." It is handicapped by the Hague conventions on warfare that prevent using expanding bullets. That isn't really as big a problem as it seems since military doctrine (at least in most civilised nations) is that it is better to wound an enemy than to kill him outright. A killing wound takes one soldier out of the fight; a non-lethal, but serious wound takes that same soldier out of the fight plus several others to care for him.

The 9mm Parabellum cartridge has been chambered in almost every type of firearm ever made. Smith & Wesson is even making revolvers chambered in 9mm these days -- and they are very good revolvers indeed. It is the overwhelmingly most common submachine gun round in the world. It is used in a great number of full-sized pistols as well as compact versions. If there is one handgun cartridge that is a true "jack of all trades" it is the 9mm Parabellum.

It is not powerful enough to use for handgun hunting, though I am sure poachers have used it. Any hunter who respects his game animal would not use it. It is a effective police and defensive use round. Personally I think the 9mm is at the low end of the acceptable power range for defensive use, but there are many who disagree with me. It has very mild recoil except when used in very lightweight pistols. Most shooters can shoot the 9mm very well. Availability of ammunition is excellent except in those countries that ban the civilian use of "military calibres."

If you are looking to buy your first centre-fire autoloading pistol, you could do a lot worse than selecting one chambered for the 9mm Parabellum.