Operation CHAOS or Operation MHCHAOS was a Central Intelligence Agency (CIA) domestic espionage project targeting American citizens operating from 1967 to 1974, established by President Lyndon B. Johnson and expanded under President Richard Nixon, whose mission was to uncover possible foreign influence on domestic race, anti-war, and other protest movements. The operation was launched under Director of Central Intelligence (DCI) Richard Helms by chief of counter-intelligence James Jesus Angleton, and headed by Richard Ober. The "MH" designation is to signify the program had a global area of operations.^{[clarification needed]}

The CIA was charged with the collection, correlation, and evaluation of intelligence. While the Act does not specify a prohibition on collecting domestic intelligence, or a restriction to only collect foreign intelligence, Executive Order 12333 of 1981 added prohibitions to limit CIA activities. The CIA began domestic recruiting operations in 1959 in the process of finding Cuban exiles who could be used in the campaign against Cuba and President Fidel Castro. As these operations expanded, the CIA formed a Domestic Operations Division in 1964. In 1965, President Lyndon Johnson requested that the CIA begin its own investigation into domestic dissent—independent of the FBI's ongoing COINTELPRO, which conducted similar activities.

The CIA developed numerous operations targeting American dissidents in the US. Many of these programs operated under the CIA's Office of Security, including:

When Nixon came to office in 1969, existing domestic surveillance activities were consolidated into Operation CHAOS. Operation CHAOS first used CIA stations abroad to report on antiwar activities of American citizens travelling abroad, employing methods such as physical surveillance and electronic eavesdropping, utilising "liaison services" in maintaining such surveillance. The operations were later expanded to include 60 officers. In 1969, following the expansion, the operation began developing its own network of informants for the purposes of infiltrating various foreign anti-war groups located in foreign countries that might have ties to domestic groups.

Eventually, CIA officers expanded the program to include other leftist or counter-cultural groups with no discernible connection to Vietnam, such as groups operating within the women's liberation movement. The domestic spying of Operation CHAOS also targeted the Israeli embassy, and domestic Jewish groups such as the B'nai B'rith. In order to gather intelligence on the embassy and B'nai B'rith, the CIA purchased a garbage collection company to collect documents that were to be destroyed.

Targets of Operation CHAOS within the anti-war movement included:

At its finality, Operation CHAOS contained files on 7,200 Americans, and a computer index totaling 300,000 civilians and approximately 1,000 groups.

The aim of the programs was to compile reports on "illegal and subversive" contacts between United States civilian protesters and "foreign elements" which "might range from casual contacts based merely on mutual interest to closely controlled channels for party directives."