Allegheny Technologies Incorporated (ATI) is a specialty metals company headquartered in Pittsburgh, Pennsylvania.

ATI produces titanium and titanium alloys, nickel-based alloys and superalloys, grain-oriented electrical steel, stainless and specialty steels, zirconium, hafnium, and niobium, tungsten materials, forgings and castings.

ATI's key markets are aerospace and defense particularly commercial jet engines (over 50% of sales), oil & gas, chemical process industry, electrical energy, and medical.

The company organizes its products into 2 segments:

Allegheny Technologies is headquartered in Downtown Pittsburgh at Six PPG Place. Steel mill plants throughout Western Pennsylvania include facilities in Harrison Township (Allegheny Ludlum's Brackenridge Works), Vandergrift, and Washington. The company also has plants in: Illinois; Indiana; Ohio; Kentucky; California; South Carolina; Oregon; Alabama; Texas; Connecticut; Massachusetts; North Carolina; Wisconsin; Shanghai, China; and several facilities in Europe.

In 1939, the merger of Allegheny Steel of Pittsburgh and Ludlum Steel of Watervliet, New York created Allegheny Ludlum Corporation; the merged company represented the manufacturers of steel for New York's Chrysler Building and Empire State Building and for the Model A Ford.

Through the 1970s, Allegheny Ludlum periodically cooperated with Ford to build several one-off promotional cars with stainless steel bodies. Three such cars are on display in the Crawford Auto-Aviation Museum.

In 1987, Allegheny Ludlum became a public company via an initial public offering.

In 1994, the company acquired Jessop Steel.

In 1996, it merged with Teledyne to form Allegheny Technologies. The company then spun off several subsidiaries as independent public companies such as Teledyne Technologies and WaterPik Technologies in 1999, to concentrate on its core business of metal and alloy production.

In 1998, the company acquired the assets of Lukens Washington Steel

In 2004, the company acquired J&L Specialty Steel

In 2005, the company sold its World Minerals subsidiary to French company Imerys.

In 2010, the company acquired Ladish Co.

Allegheny Technologies debuted its ATI 425 Titanium Alloy on June 14, 2010, at the land and air-land defense and security exhibition Eurosatory in Paris, France. The ATI 425 Titanium Alloy is developed and provided by ATI for markets that include aerospace, defense, industrial, medical and recreation.

Allegheny Ludlum's Natrona, Pennsylvania and Brackenridge, Pennsylvania plants contributed to the waste at the ALSCO Park Lindane Dump—an EPA Superfund site. These plants also released chromium into the air, which adversely affected air quality at schools in the Highlands School District.

In 2005, Allegheny Ludlum agreed to pay a $2,375,000 penalty to settle a lawsuit brought by the U.S. Department of Justice on behalf of the United States Environmental Protection Agency in 1995, which alleged that the company had unlawfully discharged oil and other pollutants, such as chromium, zinc, copper, and nickel, into the Allegheny River and Kiskiminetas River in the suburbs of Pittsburgh.