Amending the Constitution is serious business. There's a reason it's been done only 27 times over the last two centuries.

But a 28th amendment may not be far off. Lawmakers will vote soon on whether to consider a constitutional amendment that would define marriage as the legal union between one man and one woman.

The Constitution is silent on marriage now, of course, and many people think that's wise. They'd rather leave it up to the states.

As a conservative who believes in a limited federal government, I can understand that. However, in this case, we must amend the Constitution to protect it -- and the institution of marriage.

Two issues come into play here. Because of the Constitution's "full faith and credit" clause, a marriage legally sanctioned in one state is generally honored in the other 49 states. This is usually a good thing. But it means that if one state changes the very definition of marriage, that radical revision could become the law of the land in all 50 states.

An act of Congress, the federal Defense of Marriage Act of 1996, sought to ensure that states would not have to recognize another state's redefinition of marriage. Still, all it takes is one activist judge to overturn an act of Congress. And the first challenge to DOMA has been filed already. In fact, the Harvard Law Review recently said, "the time is ripe for a constitutional challenge to DOMA."

Here's the second issue. The Constitution outlines a specific separation of powers. Legislatures create laws, executives enforce them and judges interpret them. But those constitutional roles are being ignored.

First, the Vermont Supreme Court ruled that its state legislature must grant full and equal benefits of marriage to same-sex couples. Lawmakers didn't change the definition of marriage, but were forced to create "civil unions."

Then last year, the Massachusetts Supreme Judicial Court took the next step: It ruled 4-3 to redefine marriage and gave the legislature just 180 days to comply with their edict. Instead, lawmakers passed an amendment to the state constitution that effectively would overturn the court's decision. But until that amendment is ratified, the court's decision is state law. The judges have become, in effect, an unelected legislature.

Meanwhile, the mayor of San Francisco, in direct violation of state law, issued marriage licenses to 4,000 homosexual couples.

Other local executive branch officials in other states did the same thing on a smaller scale. Frighteningly, some of those entrusted with enforcing the law are all too eager to violate it for short-term political gain.

The only way to restore constitutional order is with an amendment that clearly defines marriage and counters judicial mischief.

And make no mistake: In this case, the definition matters. For millennia, marriage has been the union of a man and a woman. That's because people know instinctively that marriage benefits husbands, wives, children and all of society.

In recent decades, social science has provided proof that marriage matters. For example, a national study shows a child raised by a never-married mother is seven times more likely to live in poverty than a child raised by both biological parents in an intact marriage. Clearly, we all have a stake in maintaining and promoting traditional marriage.

That's why a constitutional amendment is an appropriate way to address this crisis: It allows the people to speak. It wouldn't leave states out of the decision-making process, since after an amendment gets the required two-thirds votes in both the House and the Senate, it must be ratified by three-quarters of the states.

And that's the point. We already know traditional marriage enjoys widespread support. A constitutional amendment will express that settled opinion, and protect a key building block of our civil society. Let the process begin.

Ed Feulner is the president of The Heritage Foundation (heritage.org), a Washington-based public policy research institute.