How did District of Columbia v. Heller change the Supreme Court’s interpretation of the Second Amendment?

In District of Columbia v. Heller (2008), the U.S. Supreme Court fundamentally shifted the interpretation of the Second Amendment by rejecting the long-standing "collective-right" theory in favor of an "individual-right" theory.1

Prior to this ruling, many interpreted the amendment as protecting only a collective right to keep and bear arms in connection with service in a militia. In a 5–4 decision, the Court held that the amendment guarantees an individual the right to possess firearms independent of militia service and to use them for traditionally lawful purposes, specifically self-defense within the home.1

Writing for the majority, Justice Antonin Scalia argued that the amendment’s operative clause codifies a pre-existing individual right derived from English common law. The Court concluded that the amendment's preamble regarding a "well regulated Militia" does not limit this individual right but rather reflects the framers' belief that an armed citizenry is essential to the security of a free state.1