Chain Reaction is a peace monument and public art sculpture composed of a metal framework of stainless steel and fiberglass surrounded by concrete, depicting a mushroom cloud created by a nuclear explosion. Designed by American editorial cartoonist Paul Conrad and built by Peter M. Carlson, the 5.5-ton, 8-meter (26-foot) high sculpture was installed in 1991 adjacent to the Santa Monica Civic Center in Santa Monica, California.

An inscription at the base of the sculpture reads, "This is a statement of peace. May it never become an epitaph." The theme of the sculpture reflects the subject of nuclear disarmament. UCLA professor Paul Von Blum places the sculpture in the category of late 20th and early 21st century contemporary American public political artwork in the tradition of commemorative works throughout the United States, calling the work "a powerful warning about the continuing dangers of nuclear war".

Conrad first expressed interest in building the sculpture in either Beverly Hills or Santa Monica in 1988. He built the sculpture with the help of an anonymous donation of $250,000 and donated the sculpture to the city of Santa Monica after it was approved by the city. It was later revealed that the donation came from philanthropist Joan Kroc, widow of Ray Kroc, the founder of the McDonald's corporation. Joan Kroc spent millions campaigning for nuclear disarmament in the 1980s. In 2012, the sculpture became the first work of public art designated as a historic landmark in the City of Santa Monica.

Conrad became the editorial cartoonist at the Denver Post in 1950. While at the Denver Post he first began to draw cartoons about peace and nuclear weapons. His cartoon depicting the ending of the atmospheric nuclear testing moratorium in 1961 was categorized by Gamson and Stuart (1992) as falling under the universal “Common Security” media frame popularized by the peace movement in the United States. These types of cartoons emphasized progress towards disarmament and “mutual cooperation, trade, cultural interaction, problem solving, and peacemaking” towards other nations, such as the Soviet Union.

He joined the Los Angeles Times in 1964 where he spent the next four decades until he retired. After criticizing president Richard Nixon during the Watergate scandal, Conrad was the only cartoonist to appear on Nixon's Enemies List. In the 1980s, Conrad criticized the military buildup and arms race advocated by president Ronald Reagan, and the involvement of the Reagan administration in the Iran–Contra affair, the illegal covert operation which sold weapons to Iran to secure the release of hostages while funding the contras in Nicaragua with the proceeds from the arms sales.

Conrad later began working as a sculptor, often donating smaller works for fundraisers. After giving a lecture, Conrad was introduced to philanthropist Joan Kroc, widow of Ray Kroc, the founder of the McDonald's corporation. Kroc was active in the anti-nuclear movement in the United States and was known as a generous patron of the arts. After becoming friends with Conrad and his wife, she anonymously contributed $250,000 to build the anti-nuclear sculpture that would become Chain Reaction.

The sculpture is based on a cartoon sketch by Conrad. According to the Chain Reaction City Landmark Assessment Report by ICF International:

the sculpture has a disheveled quality akin to the sketch-like markings and distorted proportions [of] Paul Conrad's political cartoons...this quality is conveyed by the...treatment of the stem, the irregular placement of the links, and a subtle distortion of scale between the tall stem, its pronounced bulges, and a relatively small mushroom cloud. The ability of the large brass links to catch light and define pockets of random shadow in the small spaces between them is similar in effect to the stark treatment of light [and] dark that Conrad often employed in his political cartoons.