Iran is a case in point. It has signed the Nuclear Nonproliferation Treaty, and is developing a nuclear program that it claims is for civilian purposes only. But Iran has gone far beyond what is necessary for a purely civilian program. It has concealed several nuclear facilities from the International Atomic Energy Agency, played hide-and-seek with the international community and rejected all offers of cooperation from the United States, the European Union and others. Most recently, Iran's government announced plans to enrich its uranium to levels that appear incompatible with civilian use and that defy several United Nations Security Council resolutions.

Iran also has an extensive missile development program. Iranian officials declare that the range of their modified Shahab-3 missiles is 2,000 km, putting allied countries such as Turkey, Greece, Romania and Bulgaria within reach.

In February 2009, Iran introduced the SAFIR 2 space launch vehicle. This is a key stage in the development of intermediate- and intercontinental-range missiles. If Iran completes this development, the whole of Europe, as well as all of Russia, would be within its range.

Proliferators must know that the NATO allies are unwavering in their commitment to collective defense, including nuclear deterrence. Confronted with the spread of missile technology, and unpredictable regimes and leaders, we owe it to our populations to complement our deterrence capabilities with an effective missile-defense capability.

We are not starting from scratch. NATO allies have been looking at various missile-defense options for some time. NATO itself is developing protections for our deployed troops. But with the new U.S. approach to missile defense, there are now much better opportunities for an effective NATO-wide system that would enhance the territorial defense of our populations and nations.

A true joint Euro-Atlantic missile defense would demonstrate NATO's collective will, not only to defend against the new threats of today and tomorrow, but also to send a clear message that there is nothing to be gained from missile proliferation. It can also provide an opportunity for Europeans to demonstrate again to the U.S. their willingness to invest in self-defense capabilities, and to play an active role in a process that, until now, has been conducted largely over their heads, by the U.S. and Russia.

There is another reason for developing missile defense: to create a new dynamic in European and Euro-Atlantic security. There is much talk these days about the Euro-Atlantic security architecture. Russia, in particular, has focused on treaties, conferences and political arrangements.

Clearly, these things can be useful and important. We should talk. We should look for common political approaches, many of which we have already agreed, and could easily endorse again. But, to my mind, a joint security architecture must move beyond blueprints. It needs to be built. And missile defense is a concrete way to do that.

In this respect, the news that the U.S. and Russia have agreed on a followup treaty to START that will substantially cut both countries' nuclear arsenals provides a good backdrop. This new agreement makes the world safer, and it will give impetus to cooperation with Russia in other fields, particularly NATO-Russia relations.

Since taking office last summer, I have invested considerable time and effort in revitalizing the NATO-Russia relationship, with progress made in several areas, including a joint review of common threats and challenges. But it is time to look at missile defense as another opportunity to bring us together.

We need a missile-defense system that includes not just all NATO countries, but Russia, too. The more that missile defense is seen as a shared security roof — built, supported and operated together — that protects us all, the more people from Vancouver to Vladivostok will know that they are part of one community. Such a security roof would be a strong political symbol that Russia is fully part of the Euro-Atlantic family, sharing the costs and benefits.

Of course, there are practical challenges. We would have to make our systems interoperable, share intelligence assessments and link sensitive technologies. But such cooperation is a concrete way to build trust and confidence.

For these reasons, the time has come to move forward on missile defense. We need a decision, by NATO's next summit in November, that missile defense is an Alliance mission, and that we will explore every opportunity to cooperate with Russia.

Russia also must decide to view missile defense as an opportunity, rather than a threat. If that happens, we can move forward to create a missile-defense system that not only defends the Euro-Atlantic community, but also brings it together.

The end of the Cold War has given us an enormous opportunity to achieve our goal of a Europe whole, free and at peace. We are not quite there, but we are getting there. Missile defense can be part of that positive trend.