This masterful account of the iconic American diplomat traces Acheson's extraordinary State Department years, from World War II planning and the Bretton Woods accords through the Truman Doctrine, the Marshall Plan, the North Atlantic Pact, and the Korean War. In exhaustive detail, Beisner reconstructs Acheson's pivotal role in fashioning responses to a cascade of Cold War crises and in laying down the institutional foundations of the modern postwar order. He is particularly good at bringing to life the complex personal relationships that took shape among the cast of officials surrounding Acheson; Averell Harriman, George Kennan, George Marshall, Paul Nitze, and many others appear as both colleagues and rivals as the grand policy debates unfold. Yet it is Acheson's working relationship with Harry Truman -- enduring, quietly effective, and built on deep mutual loyalty and respect -- that commands center stage and drives the story. Beisner's portrait also shows the great diplomat, a tough-minded realist in many ways, as something of a Wilsonian internationalist, reflected in Acheson's convictions about expanding the United States' "environment of freedom," fighting communism through building progressive societies, and exercising U.S. power through an array of postwar institutions. If Acheson had a core strategic belief, it was that the United States must defend its interests from a "situation of strength," which meant being uninhibited about exercising power but also patiently building partnerships and spheres of free-world cooperation. Beisner makes clear that Acheson's larger-than-life reputation is well deserved, but his book may be of more enduring value in capturing the distinctive geopolitical mindset of the 1940s -- a blend of realism and liberal idealism -- that drove the United States in its greatest foreign policy moments.