Gartner, Inc. is an American research and advisory firm providing information technology related insight for IT and other business leaders located across the world. Its headquarters are in Stamford, Connecticut, United States. It was known as Gartner Group, Inc until 2000, when it was then changed to Gartner.

Research provided by Gartner targets CIOs, senior IT, marketing and supply chain leaders. Gartner clients include large corporations, government agencies, technology companies and the investment community. The company consists of Research, Executive Programs, Consulting and Events. Founded in 1979, Gartner has over 8,100 employees, including 1,280 in research, located in 85 countries.

Gartner uses hype cycles and Magic Quadrants for visualization of its market analysis results.

The company was founded in 1979 by Gideon Gartner. Originally a private company, the Gartner Group was launched publicly the first time in the 1980s, then acquired by Saatchi & Saatchi, a London-based advertising agency, and then acquired in 1990 by some of its executives, with funding from Bain Capital and Dun & Bradstreet. The company went public again in 1993. In 2000 the name was simplified to Gartner.

Gene Hall has been the CEO of the company since August 2004.

In the course of its growth, Gartner has acquired numerous companies providing related services, including Real Decisions—which became Gartner Measurement, now part of Gartner's consulting division—and Gartner Dataquest, a market research firm. It has also acquired a number of direct competitors, including NewScience in the late 1990s, Meta Group in 2005, AMR Research and Burton Group in early 2010, and Ideas International in 2012.

In March 2014 Gartner announced that it had acquired the privately held company Software Advice for an undisclosed amount.

In July 2015, Gartner acquired Nubera, the business app discovery network that owns properties like GetApp, AppStorm, AppAppeal or CloudWork. Terms of the deal were not disclosed. In September 2015 it acquired the privately held company Capterra.

In June 2016 Gartner announced that it had acquired the privately held company SCM World, headquartered in London, U.K.

On January 5, 2017 Gartner announced it had reached an agreement to acquire CEB, Inc. in a cash and stock deal worth about US$2.6 billion.

Gartner has had a major controversy in forecasts. In 2009, Gartner predicted the PC market would experience the "sharpest unit decline in history", and a few quarters later it reported "strongest growth rate in seven years". The Actual Shipment Decline started the year 2010., reaching peak decline in 2016