The Second Amendment to the United States Constitution provides for the right to keep and bear arms, and 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."

Some people believe this language creates a Constitutional, individual right for citizens of the United States to keep and bear arms, and prohibits Congress and state legislatures from prohibiting or restricting the possession of firearms.

Others believe the beginning words ("A well regulated militia being necessary”) indicate the intent of the Amendment was only to restrict Congress from limiting a state’s right to self-defense. This collective rights theory of the Second Amendment holds that citizens do not have an individual right to possess firearms, and that federal, state, and local legislative bodies may regulate the possession of firearms without implicating a Constitutional right.

At the time the First Amendment was ratified, some militia members used their own weapons, and some used weapons from their state’s militia stores.

In Missouri, the Second Amendment of the United States Constitution is upheld, recognizing the right of individuals to keep and bear arms. This interpretation aligns with the individual rights theory, which has been reinforced by key Supreme Court decisions such as District of Columbia v. Heller (2008), where the Court held that the Second Amendment protects an individual's 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. Missouri state statutes reflect this understanding by allowing citizens to own and carry firearms with relatively few restrictions. The state has a 'shall issue' policy for concealed carry permits and has also passed legislation that allows for constitutional carry, meaning no permit is required for concealed carry by law-abiding individuals over the age of 19. Missouri law also preempts local governments from enacting more restrictive gun laws than those at the state level. However, federal and state laws still include certain regulations, such as background checks and restrictions on firearm possession for certain individuals, like felons or those adjudicated as mentally incompetent. The collective rights theory, which posits that the Second Amendment's primary intent was to ensure state militias' rights rather than individual gun ownership, has less support in current legal interpretations and is not the prevailing view in Missouri law.