The historic 5 to 4 ruling says the right to bear arms applies to individuals.
The case involved a California man who killed his ex-girlfriend after she complained to police.
In a 5-to-4 ruling, the justices decide child rape isn't a capital offense.
In a ruling Thursday, it guides federal judges to weigh conflicts of interest by insurance companies.
Justices rule 7 to 2 that some defendants aren't competent enough to represent themselves.
The US Supreme Court ruled 5 to 4 Thursday that those held in Guantánamo can challenge their detention.
Two high court rulings on Monday will complicate US efforts to prove certain crimes.
In two rulings Tuesday, the justices took an expansive view of civil rights law.