Martin Stuart Feldstein (/ˈfɛldstaɪn/ FELD-styne; November 25, 1939 – June 11, 2019) was an American economist. He was the George F. Baker Professor of Economics at Harvard University and the president emeritus of the National Bureau of Economic Research. He served as president and chief executive officer of the bureau from 1978 to 2008 (with the exception of 1982 to 1984). From 1982 to 1984, Feldstein served as chairman of the Council of Economic Advisers and as chief economic advisor to President Ronald Reagan (where his deficit hawk views clashed with the Reagan administration's large military expenditure policies). Feldstein was also a member of the Washington-based financial advisory body the Group of Thirty from 2003.

Feldstein was born in New York City to a Jewish family and graduated from South Side High School in Rockville Centre, New York. He completed his undergraduate education at Harvard University (BA, summa cum laude, 1961), where he was affiliated with Adams House, and then attended Nuffield College, Oxford (B.Litt., 1963, which was promoted by tradition to an honorary M.A. in 1963; D.Phil., 1967). He was a Research Fellow there from 1964 to 1965, an Official Fellow from 1965 to 1967, and was later an Honorary Fellow of the college.

In 1977, he received the John Bates Clark Medal of the American Economic Association, a prize which was awarded every two years until 2010 when it began to be awarded yearly. It is awarded to the economist under the age of 40 who is judged to have made the greatest contribution to economic science. That same year, he was elected to the American Academy of Arts and Sciences. In 1989, he was elected to the American Philosophical Society. He was among the ten most influential economists in the world, according to IDEAS/RePEc. He was the author of more than 300 research articles in economics and made contributions to health economics, international economics, and the economics of national security. However, he was known primarily for his greater contributions to macroeconomics, public finance and social insurance. Pioneering much of the research on the working mechanism and sustainability of public pension systems, he advanced the current understanding of the effects of social insurance. Feldstein was an avid advocate of Social Security reform and was a main driving force behind former president George W. Bush's initiative of partial privatization of the Social Security system. Aside from his contributions to the field of public sector economics, he also authored other important macroeconomics papers. One of his more well-known papers in this field was his investigation with Charles Horioka of investment behavior in various countries. He and Horioka found that in the long run, capital tends to stay in its home country — that is to say, a nation's savings is used to fund its investment opportunities. This has since been known as the "Feldstein–Horioka puzzle."^{[citation needed]}

In 1997, writing about the upcoming European monetary union and the euro, Feldstein warned that the "adverse economic effects of a single currency on unemployment and inflation would outweigh any gains from facilitating trade and capital flows" and that, while "conceived of as a way of reducing the risk of another intra-European war", it was "more likely to have the opposite effect" and "lead to increased conflicts within Europe and between Europe and the United States."

In 2003, Feldstein was awarded the Daniel M. Holland Medal in recognition of his contributions to taxation and public finance.

In 2005, Feldstein was widely considered a leading candidate to succeed chairman Alan Greenspan as Chairman of the Federal Reserve Board. This was in part due to his prominence in the Reagan administration and his position as an economic advisor for the Bush presidential campaign. The New York Times wrote an editorial advocating that Bush choose either Feldstein or Ben Bernanke due to their credentials, and the week of the nomination The Economist predicted that the two men had the greatest probability of selection out of the field of candidates. Ultimately, the position went to Bernanke, possibly because Feldstein was a board member of AIG, which announced the same year that it would restate five years of past financial reports by $2.7 billion. Subsequently, AIG suffered a serious financial collapse that played a central role in the worldwide economic crisis of 2007–2008 and the ensuing global recession. The firm was rescued only by multiple capital infusions by the U.S. Federal Reserve Bank, which extended a $182.5 billion line of credit. Although Feldstein was not explicitly linked to the accounting practices in question, he had served as a Director of AIG since 1988. In March 2007, the Lynde and Harry Bradley Foundation announced that one of four 2007 Bradley Prizes to honor outstanding achievement would be awarded to Feldstein. On September 10, 2007, Feldstein announced his resignation as president of the National Bureau of Economic Research effective June 2008.

Feldstein served as a member of the President's Foreign Intelligence Advisory Board from 2006 to 2009.

Feldstein said in March 2008 he believed the United States was in a recession and it could be a severe one.