NATO enters the eighth decade of its existence with both a longer record of success and a wider assortment of looming challenges than its founders could have foreseen when they signed the Washington Treaty in April 1949. In the thirty years since the collapse of the Soviet threat that called NATO into existence, the Western Alliance has defied innumerable predictions of its imminent demise. It ended two wars and ethnic cleansing in the Western Balkans, extended the hand of partnership to Russia and other former adversaries, stepped up to the threat of terrorism directed against NATO territory, engaged abroad including in Afghanistan, and responded with clarity, unity, and resolve to the threat posed by Russian aggression in the Euro-Atlantic region. Today, NATO stands as history’s most successful alliance, encompassing nearly a billion people and half of global GDP across a space that stretches from the Pacific coast of North America to the Black Sea.