Credibility gap is a political term that came into wide use during the 1960s and 1970s. At the time, it was most frequently used to describe public skepticism about the Johnson administration's statements and policies on the Vietnam War. Today, it is used more generally to describe almost any "gap" between the reality of a situation and what politicians and government agencies say about it.

Coinage of the term is uncertain.

"Credibility gap" was originally used in association with the Vietnam War in the New York Herald Tribune in March 1965, to describe then-president Lyndon Johnson's handling of the escalation of American involvement in the war. A number of events—particularly the surprise Tet Offensive, and later the 1971 release of the Pentagon Papers—helped to confirm public suspicion that there was a significant "gap" between the administration's declarations of controlled military and political resolution, and the reality.

The advent of the presence of television journalists allowed by the military to report and photograph events of the war within hours or days of their actual occurrence in an uncensored manner drove the discrepancy widely referred to as "the credibility gap."

However, the term had actually been used prior to its association with the Vietnam War. In December 1962, at the annual meeting of the U.S. Inter-American Council, Senator Kenneth B. Keating (R-N.Y.) praised President Kennedy's prompt action in the Cuban Missile Crisis. But he said there was an urgent need for the United States to plug what he termed the "Credibility Gap" in U.S. policy on Cuba. (Source: Associated Press article dated December 10, 1962, available online at NewspaperArchive.com.)

"Credibility gap" was, itself, a takeoff on the phrase "missile gap." This phrase was used repeatedly by John F. Kennedy during the 1960 presidential campaign to criticize the Republicans for their complacency in regard to supposed Soviet ICBM superiority. One month after Kennedy took office, he apparently discovered that the missile gap did not exist. The U.S. was, in fact, far ahead. The "missile gap" was revealed to be the product of exaggerated and possibly self-serving Air Force reports, and was spoken of no more. Thus, the phrase "credibility gap" referred back to Kennedy's credibility problems with the "missile gap."

After the Vietnam War, the term "credibility gap" has come to be used by political opponents in cases where an actual, perceived or implied discrepancy exists between a politician's public pronouncements and the actual, perceived or implied reality. For example, in the 1970s the term was applied to the discrepancy between evidence of Richard Nixon's complicity in the Watergate break-in and his repeated claims of innocence.

The Credibility Gap was a satirical comedy team comprising Harry Shearer, Richard Beebe, David L. Lander and Michael McKean. Lew Irwin, John Gilliland, Thom Beck, and Len Chandler also performed in their early days. They emerged in the late 1960s doing comedic commentary on the news for the Los Angeles AM rock radio station KRLA, and proceeded to develop more elaborate and ambitious satirical routines on the "underground" FM station KPPC, Pasadena, California.