The stage is set for a historic showdown this spring between gun enthusiasts and gun control advocates. The United States Supreme Court will hear a case in March that should determine the meaning of the Second Amendment — the hotly contested and fiercely debated part of the Constitution that guarantees "a right to keep and bear arms." The court will decide whether this guarantee protects an individual's right to have a gun for private use, or whether it only ensures a collective right to have guns in an organized military force such as a state National Guard.

The high court will review a decision of the U.S. Court of Appeals for the District of Columbia that struck down Washington, D.C.'s flat-out ban on the private possession of handguns. The District outlawed handguns in 1976 in an effort to crack down on violent crime. (The vast majority of firearms-related crime involves handguns.) D.C. residents are permitted to keep shotguns or hunting rifles at home, but even those weapons must be disassembled or have a trigger lock. The stakes are high not only for the District, but also for Chicago, which also has an outright ban on handguns, and for many states and cities nationwide that have enacted other tough restrictions on guns.

Most people are familiar with the Second Amendment's phrase that "the right of the people to keep and bear arms shall not be infringed." But the Second Amendment's full text states: "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." In the past, lower courts, focusing on the amendment's opening phrase, have ruled that it protects only a state's authority to maintain "a well-regulated militia," not an individual's right to own a gun for his or her private use. In fact, the D.C. Court of Appeals ruling that is now before the Supreme Court marks the first time a federal appeals court has ever declared that a gun law violated the Second Amendment.

In its only other decision directly involving the Second Amendment, rendered almost 70 years ago, the Supreme Court upheld a man's conviction for transporting a sawed-off shotgun across state lines, ruling that possession of such weapons was not protected by the Second Amendment, whose "obvious purpose" is the "preservation or efficiency of a well-regulated militia." United States v. Miller (1939). Proponents of gun bans frequently cite this earlier decision, but many court observers believe that the current Supreme Court will overturn or limit this precedent.

Those in favor of restrictions on firearms argue that a plain reading of the text of the Second Amendment, as well as the Amendment's history, demonstrates that the Amendment was concerned with state militias, not with the rights of individuals. They point out that, at the time the Second Amendment was drafted, most states were concerned with maintaining a viable state militia to defend the state against any possible invasion. They also point out that the use of the phrase "to keep and bear arms" was explicitly a military phrase, lending further support for their position that the amendment must be understood as only protecting the collective right to arm a militia.

On the other side of the debate are many gun owners, led by the National Rifle Association and the gun lobby. They argue that the Second Amendment was intended to protect the rights of individual Americans to defend themselves, not only to protect the rights of the states to form militias. They point out that the Bill of Rights, the first ten amendments to the U.S. Constitution of which the Second Amendment is a part, was almost entirely a declaration of individual rights intended to protect personal liberty. (Even if the court strikes down the D.C. law and rules that individuals have a constitutional right to possess handguns, its decision is not likely to void all firearms regulations, such as those regulating concealed weapons and forbidding convicted felons from owning guns.)

The one point on which experts agree is that the Supreme Court's ruling in District of Columbia v. Heller may be the most important decision on gun control in our nation's history.

Rhonda Brownstein is the director of the Southern Poverty Law Center's Legal Department.