The National Guardian (later known as The Guardian) was a radical leftist weekly newspaper published in New York City between 1948 and 1992. The paper was founded by James Aronson, Cedric Belfrage, and John T. McManus with the purpose of providing an alternative perspective to the mainstream media during the Cold War. The paper's early years focused on and supported New Deal programs and the New York American Labor Party (ALP). The National Guardian reported on labor, activism, reform, and social movements without particular party affiliations, advocating for a unified leftist party in the United States. Known for its independent and investigative journalism, the paper produced significant pieces on civil rights and the Cold War, and was one of the few publications to print news sympathetic to Julius and Ethel Rosenberg during their trial and execution, with much of the paper's reporting coming from William A. Reuben.

During the 1960s, the paper shifted directions toward the New Left, with Aronson selling his shares and the publication changing its name to the Guardian. In the 1970s, the Guardian supported Marxism-Leninism, calling for a new Marxist-Leninist party in the United States. The paper established Guardian Clubs for readers in the 1980s, which gave rise to competitor publications Frontline and Line of March. After years of declining circulation and financial difficulties, the paper ceased publication in 1992.