United Technologies Corporation (UTC) is an American multinational conglomerate headquartered in Farmington, Connecticut. It researches, develops, and manufactures products in numerous areas, including aircraft engines, aerospace systems, HVAC, elevators and escalators, fire and security, building systems, and industrial products, among others. UTC is also a large military contractor, getting about 10% of its revenue from the U.S. government. Gregory J. Hayes is the CEO and chairman.

In 1974, Harry Gray left Litton Industries to become the CEO of United Aircraft. He pursued a strategy of growth and diversification, changing the parent corporation's name to United Technologies Corporation (UTC) in 1975 to reflect the intent to diversify into numerous high tech fields beyond aerospace. (The change became official on May 1, 1975.) The diversification was partially to balance civilian business against any overreliance on military business. UTC became a mergers and acquisitions (M&A)–focused organization, with various forced takeovers of unwilling smaller corporations. The next year (1976), UTC forcibly acquired Otis Elevator. In 1979, Carrier Refrigeration and Mostek were acquired; the Carrier deal was forcible, while the Mostek deal was a white knight move against hostile takeover designs by Gould.

At one point the military portion of UTC's business, whose sensitivity to "excess profits" and boom/bust demand drove UTC to diversify away from it, actually carried the weight of losses incurred by the commercial M&A side of the business. Although M&A activity was not new to United Aircraft, the M&A activity of the 1970s and 1980s was higher-stakes and arguably unfocused. Rather than aviation being the central theme of UTC businesses, high tech (of any type) was the new theme. Some Wall Street watchers questioned the true value of M&A at almost any price, seemingly for its own sake.

Mostek was sold in 1985 to the French electronics company Thomson.

UTC acquired Sundstrand Corporation in 1999, and merged it into UTC's Hamilton Standard unit to form Hamilton Sundstrand.

In 2003, UTC entered the fire and security business by purchasing Chubb Security.

In 2004, UTC acquired the Schweizer Aircraft Corporation which planned to operate as a wholly owned subsidiary under their Sikorsky Aircraft division.

In 2005, UTC further pursued its stake in the fire and security business by purchasing Kidde. Also in 2005, UTC acquired Boeing's Rocketdyne division, which was merged into the Pratt & Whitney business unit.

In 2007, UTC opened the Hawk Works, a Rapid Prototyping and Military Derivatives Completion Center (RPMDCC) located west of the Elmira-Corning Regional Airport in Big Flats, NY.

In March 2008, UTC made a $2.63 billion bid to acquire Diebold, a Canton, Ohio based manufacturer of banking and voting machines. Diebold rejected the buyout bid as inadequate.

In November 2008, UTC's Carrier Corporation acquired NORESCO, which is one of the nation's largest energy service companies.

In December 2009, it was announced that UTC would acquire a 49.5% stake in Clipper Windpower for $206 million.

In April 2010, UTC announced that it was investing €15 million ($20 million) to set up the United Technologies Research Centre Ireland in University College Cork which will carry out research on energy and security systems.

In October 2010, UTC agreed with Clipper to acquire the rest of the company.

In September 2011, UTC acquired a $18.4 billion deal (including $1.9 billion in net debt assumed) for aircraft components maker Goodrich Corporation.

In June 2012, it was discovered that UTC sold military technology to the Chinese. For pleading guilty to violating the Arms Export Control Act and making false statements, United Technologies and its subsidiaries were fined $75 million.

In July 2012, United Technologies acquired Goodrich and merged it with Hamilton Sundstrand; the resulting organization is UTC Aerospace Systems.

In February 2013, UTC Power was sold to ClearEdge Power.

In October 2014, Toshiba and United Technologies made a deal to expand their joint venture outside Japan.

In January 2015, UTC Building & Industrial Systems completed the acquisition of CIAT Group, a leading HVAC manufacturing company in France. In November, Lockheed Martin completed its $9.0 billion acquisition of Sikorsky Aircraft.

In February 2016, UTC subsidiary Carrier Air Conditioner announced to employees at its Indianapolis plant that Carrier is moving manufacturing to Mexico: “The best way to stay competitive and protect the business for long-term is to move production from our facility in Indianapolis to Monterrey, Mexico.” In December, Carrier agreed to keep the Indianapolis plant open, keeping 1,100 jobs in Indianapolis.

On September 4, 2017, proposed to acquire Rockwell Collins in cash and stock for $23 billion, $30 billion including Rockwell Collins' net debt, for $500+ million of synergies expected by year four.

Hartford's Gold Building served as UTC's headquarters from 1975–2015

Otis Elevator's former headquarters serve as UTC's headquarters since 2015

During the 2004 election cycle, UTC was the sixth largest defense industry donor to political campaigns, contributing a total of $789,561. Sixty-four percent of UTC's 2004 contributions went to Republicans. UTC was also the sixth largest donor to federal candidates and political parties in the 2006 election cycle. Thirty-five percent of those contributions went to Democrats; 53% of the funds were contributed to Republicans.

In 2005, United Technologies was among 53 entities that contributed the maximum of $250,000 to the second inauguration of President George W. Bush.

In 1981, a contribution from UTC made possible the exhibition "Paris/Magnum: Photographs 1935–1981", featuring photographs of Paris taken by photographers of Magnum Photos, the agency founded in 1947 by Robert Capa, George Rodger, Henri Cartier-Bresson, William Vandivert, and David Seymour. A volume of the same title, with text by Irwin Shaw and an introduction by Inge Morath, was also published in 1981.

UTC is the sponsor of the exhibition "Aphrodite and the Gods of Love" at Boston's Museum of Fine Arts that opened in fall 2011.

UTC and its subsidiaries are major contributors to museums such as the New England Air Museum.

Researchers at the University of Massachusetts Amherst have identified UTC as the 38th-largest corporate producer of air pollution in the United States as of 2008. UTC released roughly 110,000 pounds of toxic chemicals annually into the atmosphere including manganese, nickel, chromium and related compounds.

In the 2016 University of Massachusetts Amherst Toxic 100 Air Polluters Index, UTC was ranked 9th by a toxicity population exposure score. It was also reported they release 60,000 pounds of toxins into the air, the second lowest amount by the top 10 listed companies.