This dissertation examines the Cold War writings and activities of the American commentator Walter Lippmannin particular his observations about U.S. policy in Vietnam. Lippmann was the preeminent columnist of his era, writing 2,300 installments of his Today and Tomorrow column between 1945 and 1967. Lippmann crafted a conceptual framework for promoting American internationalism that blended political realism, cosmopolitanism, and classical diplomacy. That approach shaped his role as a moderator of the domestic and international dialogue about the Cold War, as a facilitator of ideas and policies, and as a quasi-diplomat. Chapter one suggests that based on new archival sources a re-evaluation of Lippmann is necessary to correct inadequacies in the standard literature. Chapter two surveys his strategic internationalist approach to foreign affairs from the publication of his first foreign policy book in 1915 to three influential volumes he wrote between 1943 and 1947. Chapter three explores Lippmann's position on a prominent and controversial Cold War issuethe partition of Germany. Chapter four makes a comparative analysis of Lippmann with the French commentator Raymond Aron, examining Lippmann's part as a dialogue-shaper and public broker during the Cuban Missile Crisis and the subsequent debate about nuclear sharing in the Atlantic Alliance. Chapter five moves the study toward his writings on U.S. policy in Asiaparticularly U.S.-China policy and the Korean War. Chapter six examines Lippmann's analyses of U.S.-Vietnam policy from 1949 to 1963 framed by three consistent arguments: first, that America had no vital interests at stake there; second, that it could not win a military victory there at any reasonable cost; and, third, that its best course was to use diplomacy to promote Vietnamese neutralism. Chapter seven explores Lippmann's efforts to dissuade U.S. officials from intervention in 1964. Chapter eight details policymakers' elaborate efforts to delay Lippmann's public criticisms of the Vietnam policies. Chapter nine explores the Johnson administration's determination to discredit Lippmann's public criticisms of the war after July 1965. Chapter ten counters the standard literature's portrayal of Lippmann's Cold War commentary and suggests that his most influential activity as a public figure may have been as a quasi-diplomatist.