Walt Whitman Rostow (also known as Walt Rostow or W.W. Rostow) (October 7, 1916 – February 13, 2003) was a United States economist and political theorist who served as Special Assistant for National Security Affairs to U.S. President Lyndon B. Johnson.

Prominent for his role in the shaping of US foreign policy in Southeast Asia during the 1960s, he was a staunch anti - communist, and was noted for a belief in the efficacy of capitalism and free enterprise. Rostow served as a major adviser on national security affairs under the Kennedy and Johnson administrations. He strongly supported US involvement in the Vietnam War. In his later years he taught at the Lyndon B. Johnson School of Public Affairs at the University of Texas at Austin with his wife, Elspeth Rostow, who would later become dean of the school. He wrote extensively in defense of free enterprise economics, particularly in developing nations. Rostow wrote a book The Stages of Economic Growth: A non-communist manifesto (1960) which was used in several fields of social sciences.

His older brother, Eugene Rostow, also held a number of high government foreign policy posts.

Walt Rostow was born in New York City to a Russian Jewish immigrant family. His parents, Victor and Lillian Rostow, were active socialists and their three sons, Eugene Victor Debs Rostow, Ralph Waldo Emerson Rostow and Walt Whitman Rostow, were named after Eugene V. Debs, Ralph Waldo Emerson, and Walt Whitman. Rostow entered Yale University at age 15 on a full scholarship, graduated at 19, and completed his Ph.D. there in 1940. He also won a Rhodes Scholarship to study at Balliol College, Oxford, where he completed a B.Litt. degree. In 1936, during the Edward VIII abdication crisis, he assisted the broadcaster Alistair Cooke, who reported on the events for the NBC radio network. After completing his education he started teaching economics at Columbia University.

During World War II he served in the Office of Strategic Services under William Joseph Donovan. Among other tasks, he participated in selecting targets for U.S. bombardment. (Nicholas Katzenbach would later joke, "I finally understand the difference between Walt and me [...] I was the navigator who was shot down and spent two years in a German prison camp, and Walt was the guy picking my targets.") Rostow became Assistant Chief of the German - Austrian Economic Division in the United States Department of State in Washington, D.C., immediately after the war. From 1946 to 1947, he returned to Oxford to teach as the Harmsworth Professor of American History. Rostow became the Assistant to the Executive Secretary of the Economic Commission for Europe in 1947, and was involved in the development of the Marshall Plan.

He spent a year in 1949 at Cambridge University as the Pitt Professor of American History and Institutions. Rostow was Professor of Economic History at the Massachusetts Institute of Technology from 1950 to 1961 and a staff member of the Center for International Studies, MIT, from 1951 to 1961. In 1958, he became a speechwriter for President Dwight D. Eisenhower.

In 1960 Rostow joined John F. Kennedy's presidential campaign, helping to coin such memorable campaign phrases as "Let's get this country moving again," "The New Frontier," and "The Development Decade." His ability to couch concepts in terms accessible to the layman was a strong suit.

In 1961, President John F. Kennedy appointed Rostow as Deputy Special Assistant to the President for National Security Affairs, reporting to McGeorge Bundy. Late in 1961, he was then appointed as counselor of the Department of State and Chairman of the Policy Planning Council, Department of State. Rostow was appointed by Johnson in May 1964 to be U.S. Member of the Inter - American Committee on the Alliance for Progress (CIAP).

In early 1966, he was named special Assistant for National Security Affairs (the post now known as National Security Advisor) where he was a main figure in developing the government's policy in the Vietnam War, and where he remained until February 1969. Pulitzer Prize - winning journalist David Halberstam noted of Rostow's time as Assistant for National Security Affairs,

"He became the president's national security adviser at a time when criticism and opposition to the war were beginning to crystallize, and he eventually served the purpose of shielding the president from criticism and from reality."

His anti communist and pro-free enterprise views made him highly unpopular in the social sciences sector of US academia, which has mostly left wing beliefs. Because of his hawkish stance, Rostow was a pariah in many academic quarters, and was not invited back to MIT after his government service. Instead he landed at the Lyndon B. Johnson School of Public Affairs at the University of Texas, where he served as the Rex G. Baker Jr. Professor Emeritus of Political Economy. He and his wife Elspeth Rostow, created "The Austin Project", a model for at risk, low income youth. He continued to teach history and economics until his death in 2003 at the age of 86.

Rostow developed the Rostovian take-off model of economic growth, one of the major historical models of economic growth. The model argues that economic modernization occurs in five basic stages of varying length — traditional society, preconditions for take-off, take-off, drive to maturity, and high mass consumption. This became one of the important concepts in the theory of modernization in the social evolutionism. He received the Order of the British Empire (1945), the Legion of Merit (1945), and the Presidential Medal of Freedom (1969).