This chapter surveys Supreme Court decisions involving the Second Amendment right “to keep and bear arms.” Nowhere is the current Court’s approach more originalist. Before 2008, the Court had never held that the Second Amendment protects a personal right to possess weapons unrelated to service in what the Amendment’s preamble characterizes as the need of “free states” for “a well-regulated militia.” This chapter describes events leading to the Court’s turnaround and analyzes its decisions since then. In applying other constitutional guarantees, the Court frequently asks whether restrictions are “narrowly tailored” to important or “compelling” governmental interests. By contrast, it insists that the permissibility of modern regulations of firearms depends exclusively on whether analogous restrictions were historically tolerated. In response to difficulties that the lower courts encountered in determining whether challenged regulations had historical analogues, the Court recently explained that precise factual similarity matters less than whether a modern restriction is “consistent with the principles that underpin our regulatory tradition.” Applying that test poses formidable challenges. But if the Court’s majority views its prescribed approach to defining Second Amendment rights as successful, it could imaginably extend its exclusive reliance on history and tradition to identify constitutional violations to other areas.