You can take your state-of-the-art Glock straight out of the box and start shooting. And that's what you should do if you plan on using it for personal defense. Nothing you can do will make it work any better in that definitive role than it already does. But what if you want something that makes your Glock a little different from everybody else's, a little more suited to your specialized needs? The same design simplicity that makes the Glock easy to manufacture and use also makes it easy to customize.