"Well regulated militia" appears in the 2nd Amendment''s opening clause: "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." Framers used "militia" to describe part-time citizen soldiers who trained periodically and could be called up during emergencies, as opposed to professional standing armies they distrusted. "Well regulated" meant properly trained and disciplined, not restricted by extensive rules—colonial militias drilled regularly and followed military codes. The militia clause sparked 200 years of debate: does it limit gun rights to militia service, or does it explain why an individual right exists? The Supreme Court resolved this in D.C. v. Heller (2008), ruling the 2nd Amendment protects an individual right to own guns unconnected to militia service, while governments can still regulate who owns weapons and where they''re carried. Justice Scalia''s majority opinion treated the militia clause as prefatory (explanatory) rather than operative (binding). Critics note the Framers put the militia clause first, suggesting it mattered to the right''s scope. Today, state National Guard units descend from colonial militias, but the militia clause plays no role in modern gun jurisprudence.