During the twentieth century, Harvard's international reputation grew as a burgeoning endowment and prominent professors expanded the university's scope. Explosive growth in the student population continued with the addition of new graduate schools and the expansion of the undergraduate program. Radcliffe College, established in 1879 as sister school of Harvard College, became one of the most prominent schools for women in the United States.

James Bryant Conant (president, 1933–1953) reinvigorated creative scholarship to guarantee its preeminence among research institutions. He saw higher education as a vehicle of opportunity for the talented rather than an entitlement for the wealthy, so Conant devised programs to identify, recruit, and support talented youth. In 1943, he asked the faculty make a definitive statement about what general education ought to be, at the secondary as well as the college level. The resulting Report, published in 1945, was one of the most influential manifestos in the history of American education in the 20th century.

In 1945-1960 admissions policies were opened up to bring in students from a more diverse applicant pool. No longer drawing mostly from rich alumni of select New England prep schools, the undergraduate college was now open to striving middle class students from public schools; many more Jews and Catholics were admitted, but few blacks, Hispanics or Asians.

Harvard and its affiliates, like many American universities, are considered by some to be politically liberal (left of center).[28] Conservative author William F. Buckley, Jr. quipped that he would rather be governed by the first 2000 names in the Boston phone book than by the Harvard faculty, Richard Nixon famously referred to Harvard as the "Kremlin on the Charles" around 1970, and Vice President George H.W. Bush disparaged what he saw to be Harvard's liberalism during the 1988 presidential election.[31] Republicans remain a small minority of faculty, and the University has refused to officially recognize the Reserve Officers' Training Corps (ROTC) program — forcing students to commission through nearby MIT.The Harvard College Handbook explains, "Current federal policy of excluding known lesbian, gay, and bisexual individuals from admission to ROTC or of discharging them from service is inconsistent with Harvard’s values as stated in its policy on discrimination."

President Lawrence Summers resigned his presidency in 2006. His resignation came just one week before a second planned vote of no confidence by the Harvard Faculty of Arts and Sciences. Former president Derek Bok served as interim president. Members of Harvard's Faculty of Arts and Sciences, which instructs graduate students in GSAS and undergraduates in Harvard College, had passed an earlier motion of "lack of confidence" in Summers' leadership on March 15, 2005 by a 218-185 vote, with 18 abstentions. The 2005 motion was precipitated by comments about the causes of gender demographics in academia made at a closed academic conference and leaked to the press.[34] In response, Summers convened two committees to study this issue: the Task Force on Women Faculty and the Task Force on Women in Science and Engineering. Summers had also pledged $50 million to support their recommendations and other proposed reforms. Drew Gilpin Faust is the 28th president of Harvard. An American historian, former dean of the Radcliffe Institute for Advanced Study, and Lincoln Professor of History at Harvard University, Faust is the first female president in the university's history.