The Second Amendment reads: “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.”
According to the Supreme Court of the United States in the decision in DISTRICT OF COLUMBIA ET AL. v. HELLER, generally referred to as the Heller decision. The court held that “The Second Amendment protects an individuals 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.” (Heller, p.1) Later, the Court affirmed that this right extended to residents of the several states in the decision in MCDONALD ET AL. v. CITY OF CHICAGO, ILLINOIS, et. Al. generally called the McDonald Decision, and held: “the Court . . . concluding that the Fourteenth Amendment incorporates the Second Amendment right, recognized in Heller, to keep and bear arms for the purpose of self-defense.” (McDonald, p. 2)
The court however does go on to state that the right to keep and bear arms as stated in the Second Amendment is not unlimited. The government does have a compelling interest in limiting who may purchase and have a firearm. For example, felons and the mentally ill may not bear arms. Nor does the Heller decision change any laws limiting where firearms may be carried, such as sensitive locations as government building and schools. Nor does Heller or McDonald allow for purchase of previously outlawed weapons such as the full automatic machine guns, or illegally shortened shotguns. Further Heller does not change the conceal carry laws of the several states.
What Heller and McDonald decisions state is that to have and keep a functioning legal firearm in the home to be used in self-defense is an inalienable right on the same level as the freedom of speech and religion as established in the First Amendment.
While some gun control advocates have placed an emphasis on the first clause of the Second Amendment: “A well regulated Militia, being necessary to the security of a free State. . .” indicating that the Second Amendment only applies to the states and refers to the state militias, which are now organized as the National Guard. However, the Court held: “The Amendment’s prefatory clause announces a purpose, but does not limit or expand the scope of the second part, the operative clause. The operative clause’s text and history demonstrate that it connotes an individual right to keep and bear arms.” (Heller, p. 1-2)
Sources:
http://www.scotusblog.com/wp-content/uploads/2008/06/07-290.pdf
http://www.supremecourt.gov/opinions/09pdf/08-1521.pdf
http://www.archives.gov/exhibits/charters/bill_of_rights_transcript.html