Nicholas Gregory Mankiw (; born February 3, 1958) is an American macroeconomist who is currently the Robert M. Beren Professor of Economics at Harvard University. Mankiw is best known in academia for his work on New Keynesian economics.

Mankiw has written widely on economics and economic policy. As of February 2020, the RePEc overall ranking based on academic publications, citations, and related metrics put him as the 45th most influential economist in the world, out of nearly 50,000 registered authors. He was the 11th most cited economist and the 9th most productive research economist as measured by the h-index. In addition, Mankiw is the author of several best-selling textbooks, writes a popular blog, and has since 2007 written approximately monthly for the Sunday business section of The New York Times. According to the Open Syllabus Project, Mankiw is the most frequently-cited author on college syllabi for economics courses.

Mankiw is a conservative and has been an economic adviser to several Republican politicians. From 2003 to 2005, Mankiw was Chairman of the Council of Economic Advisers under President George W. Bush. In 2006, he became an economic adviser to Mitt Romney, and worked with Romney during his presidential campaigns in 2008 and 2012. In October 2019, he announced that he was no longer a Republican because of his discontent with President Donald Trump and the Republican Party.