In Ikenberry’s splendid new book—his most impressive work to date—he defends liberal internationalism against realists who dismiss it as utopianism and radicals who deride it as window-dressing for capitalist imperialism. Ikenberry argues that liberal internationalism is in fact a pragmatic political project whose core purpose has always been to promote a cooperative world in which free societies can defend themselves and address shared problems. He traces the tradition’s rich intellectual and diplomatic history, from its Enlightenment origins to its troubled path in the twenty-first century, identifying its enduring elements of open trade, international law and institutions, cooperative security, and progressive social aspirations. Liberal internationalism appears to be on the ropes today, pummeled by populists who reject globalization, nationalists who demand untrammeled sovereignty, and geopolitical rivals (led by China) who peddle competing global models. Many saw the 2016 election of U.S. President Donald Trump as a knockout blow. Appearances, however, can be deceiving. As Ikenberry reminds us, the liberal world order has suffered crises in the past, which challenged its champions to reimagine how a new world order might be constructed. In each case, they rose to the occasion. This book is a fitting capstone to an enviable career—although surely not Ikenberry’s last word on the subject.