[ChefKeith]

A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed.

The People ARE the Militia, not the National Guard.

What part don't you understand?

[El Gato]

The People ARE the Militia, not the National Guard.

Strictly speaking, the National Guard, when not federalized, form the Organized Militia, or at least a part of it in states which have a State Guard.

Here is the definition of the militia in federal law. Basically all males 17 to 45 and all female members of the National Guard. (And male guardsmen beyond those ages as well) YMMV depending on your state, in Texas it's all persons, save a few public officials, from (approximately) 18 to 60. Even the old Cat has a few more years in the Texas militia.