The Monthly Review is an independent socialist magazine published monthly in New York City. Founded in 1949, it is the longest continuously published socialist magazine in the U.S. From its beginning, Monthly Review was characterized as having "a nondoctrinaire approach to socialism" that became increasingly critical of the Soviet Union. The magazine was most closely linked to Third World socialism and national liberation struggles, and consequently saw its popularity grow among the New Left during the Vietnam War.

Following the failure of Progressive Party candidate Henry A. Wallace in the 1948 presidential election, two former Wallace supporters, and ex-Harvard colleagues, met on a New Hampshire farm where one of them was living. The two men were literary scholar and Christian socialist F. O. "Matty" Matthiessen and Marxist economist Paul Sweezy. Matthiessen, who came into an inheritance after his father died in a car accident in California, had no pressing need for the inheritance money. He offered Sweezy to underwrite "that magazine [Sweezy] and Leo Huberman were always talking about" by committing the sum of $5,000 per year for three years.

While Matthiessen was the angel investor of the new publication, the editorial responsibilities were handled by Sweezy and his friend Leo Huberman. The latter was a New York University-educated author of left-wing books and pamphlets during the 1930s and '40s. He worked full-time on the Monthly Review from its establishment until his death of a heart attack in 1968.

Sweezy and Huberman were complementary figures guiding the publication. Sweezy's theoretical bent and writing ability were put to use for a majority of the editorial content; Huberman took charge of the business and administrative aspects of the enterprise. Sweezy remained at home in New Hampshire, traveling to New York City once a month to read manuscripts, whereas Huberman conducted the magazine's day-to-day operations along with his wife, Gertrude Huberman, and family friend Sybil Huntington May.

Briefly joining Sweezy and Huberman as a third founding editor of Monthly Review — although not listed as such on the publication's masthead — was German émigré Otto Nathan (1893–1987). While his time with the magazine was short, he was instrumental in obtaining the lead piece for the debut May 1949 issue: Albert Einstein's essay "Why Socialism?". Another key contributor during the magazine's first 15 years was economist Paul Baran, frequently considered as the third member of an editorial troika including Sweezy and Huberman.

Monthly Review launched in 1949 with only 450 subscribers, most of whom were acquaintances of Huberman or Sweezy. The magazine's ideology and readership paralleled that of the independent socialist weekly newspaper The National Guardian, established in 1948. Despite a prevailing conservative political climate in the U.S., Monthly Review quickly reached a critical mass of subscribers, with its paid circulation rising to 2,500 in 1950, and to 6,000 by mid-decade.

During the McCarthyism era in the early 1950s, editors Sweezy and Huberman were targeted for "subversive activities". Sweezy was teaching then at the University of New Hampshire. After being subpoenaed by New Hampshire Attorney General Louis C. Wyman, Sweezy refused to answer questions about his lecture notes or political beliefs. He was found in contempt of court. He appealed the conviction to the U.S. Supreme Court, which ruled in his favor in Sweezy v. New Hampshire.

In the 1950s, Monthly Review deviated from its non-graphic look by featuring labor cartoonist Fred Wright. The magazine added veteran radical Scott Nearing to its ranks in 1953. For nearly 20 years, he authored a column titled "World Events". Throughout the Truman and Eisenhower administrations, the magazine published a variety of left-wing intellectuals such as pacifist activist Staughton Lynd (1952), historian William Appleman Williams (1952), and sociologist C. Wright Mills (1958).