The Supreme Court of the United States, in 554 U. S. ____ (2008) DISTRICT OF COLUMBIA v. HELLER [PDF], has said (quoting from the syllabus (headnote) of the Opinion):
The Second Amendment protects an individual right to possess a firearm unconnected with service in a militia, and to use that arm for traditionally lawful purposes, such as self-defense within the home.
The handgun ban and the trigger-lock requirement (as applied to self-defense) violate the Second Amendment. The District’s total ban on handgun possession in the home amounts to a prohibition on an entire class of “arms” that Americans overwhelmingly choose for the lawful purpose of self-defense. Under any of the standards of scrutiny the Court has applied to enumerated constitutional rights, this prohibition—in the place where the importance of the lawful defense of self, family, and property is most acute—would fail constitutional muster. Similarly, the requirement that any lawful firearm in the home be disassembled or bound by a trigger lock makes it impossible for citizens to use arms for the core lawful purpose of self-defense and is hence unconstitutional.
Read the PDF for the actual opinion, taking note of what is not covered, such as registration, gun-free areas, etc.
Wikipedia has an extensive entry on firearms.
Also see Happiness is a Warm Gun.
image: Bobbfwed, HK USP 45.jpg, Wikimedia Commons