AECOM (/eɪ.iːˈkɒm/ ay-ee-KOM) (formerly known as AECOM Technology Corporation) is an American multinational engineering firm that provides design, consulting, construction, and management services to a wide range of clients.

AECOM has approximately 87,500 employees, and is number 156 on the 2016 Fortune 500 list. Fortune named AECOM as one of 2015 World's Most Admired Companies, and again in 2016 & 2017. Engineering News-Record ranked AECOM as Number 1 Global Design Firm.

The company's official name from 1990 to early January 2015 was AECOM Technology Corporation. Today, it is known simply as AECOM. The company is listed on the New York Stock Exchange (NYSE) under the ticker symbol ACM and on the Frankfurt Stock Exchange under the ticker symbol E6Z.

Operating through more than a dozen subsidiaries, AECOM traces its origins to Kentucky-based Ashland Oil & Refining Company, which in turn grew out of Swiss Drilling Company, founded in Oklahoma in 1910 by J. Fred Miles. He gained control of some 200,000 acres and formed Swiss Oil Company in Lexington. In 1924 Miles launched a refining operation called Ashland Refining Company, headed by Paul Blazer. While the parent company struggled, leading to the ouster of Miles, Ashland prospered under Blazer's leadership, and in 1936 he was named chief executive officer of the reorganized company, Ashland Oil & Refining Company. In 1966 Ashland acquired Warren Brothers and became involved in highway construction and construction materials. The company was able to take advantage of refinery byproducts to produce asphalt. Ashland grew into one of the nation's major road-construction firms, and laid a foundation for AECOM. Through a series of acquisitions and technological developments prior to the buyout, Ashland grew to include chemical, petrochemical, highway construction, and construction materials firms within its realm, laying the groundwork for the creation of Ashland Technology in 1985.

In the 1970s Ashland Oil & Refining became Ashland Oil, Inc. Five years later the company consolidated its construction assets into a construction division and also formed a coal subsidiary, indicative of a changing focus at Ashland. Although it generated more than $1 billion a year in sales, Ashland was a small player in the oil industry at a time when the cost of exploration was prohibitively expensive. By 1980 Ashland sold its production assets, and a year later was reorganized as a modified holding company. A new corporate strategy was implemented as Ashland now focused on refining and marketing, and sought to grow its non-refining businesses. In 1984 Ashland acquired Daniel, Mann, Johnson & Mendenhall (DMJM), a global provider of transportation-related engineering services. Originally focused on military projects, after World War II it had become one of the first integrated engineering and architectural firms in the western United States. The acquisition of DMJM also included its president, Richard G. Newman, AECOM's future chief executive and chairman. In 1985 DMJM became part of a new subsidiary, Ashland Technology Corporation. Two years later Newman was named its new president.

When Ashland chose to return to its core petroleum refining business in the late 1980s, Newman recommended an employee buyback proposal, resulting in the spin-off of Ashland Technology and the creation of AECOM (Architecture, Engineering, Consulting, Operations, and Maintenance) in 1990. The company went on to acquire a number of engineering, design and planning firms including engineering company Maunsell, urbanism and sustainability practice EDAW, Economic Research Associates (ERA), environmental management firm ENSR and The RETEC Group Inc., architects Ellerbe Becket and Davis Langdon, the quantity surveyors and construction consultants.

AECOM went public during May 2007 with an initial public offering on the NYSE, netting $468.3 million. On January 8, 2008 AECOM acquired The Services Group, Inc., a provider of consulting services to the US Agency for International Development and other multi-lateral donor organizations. On July 28, 2008, AECOM completed its purchase of Earth Tech Inc., a consulting and engineering firm, from Tyco International for $510 million. On July 14, 2010, AECOM announced its acquisition of Tishman Construction Corp., a leading provider of construction management services in the United States and the United Arab Emirates, in a $245 million transaction including $202 million in cash and the remainder in AECOM common stock. On July 13, 2014, AECOM announced its acquisition of URS Corporation, an engineering, construction, and technical services firm for US$56.31 per share in cash and stock. Effective July 10, 2014, it acquired ACE International Consultants SL, a Madrid-based provider of consulting services. In July 2014, it acquired Hunt Construction Group, adding to AECOM's construction services business.

AECOM's first president and CEO was Richard Newman, who came to Ashland through its acquisition of DMJM. Newman served as president of Ashland Technology and was instrumental in the creation of AECOM.

In 2005, John M. Dionisio succeeded Newman as president and CEO of AECOM. In 2011, Dionisio became chairman of the company. In March 2014, Michael S. Burke succeeded Dionisio and serves as the company's current chairman and CEO. Dionisio remains on AECOM's Board of Directors.

In 2011, Stephen M. Kadenacy was named chief financial officer and currently serves as president. In 2017 Kadenacy was succeeded by Randy Wotring.

In May 2014, Kevin Lynch was appointed as executive vice president and chief strategy officer at AECOM.

In March 2015, Carla Christofferson was appointed as executive vice president and general counsel of the firm.

In August 2015, Mary E. Finch was named executive vice president and chief human resources officer, effective September 28.

AECOM provides professional technical and management support services to both public and private sector clients. AECOM currently works in the following areas: the Americas, Europe, Asia, Middle East, Africa, and Australia/New Zealand. Services relate to areas including Architecture & Design, Asset Management, Construction, Cost Management, Decommissioning & Closure, Economics, Engineering, Environmental Services, International Development, IT & Cyber Security, Operations & Maintenance, Planning & Consulting, Program, Management/Construction Management, Risk Management & Resilience and Technical Services.

AECOM is headquartered in Los Angeles, California, United States, with clients in more than 150 countries. The company reported a revenue of US$17.4 billion during the 12 months that ended September 30, 2016.

AECOM provides Specialized Integrated Solutions in Alternative Delivery Models, Cities Solutions, Converged Resilience, Equity Investment, Multinational Investment &, Development, Process Technologies and Public-Private Partnerships. The company operates under the following business lines: Architecture; Building Engineering; Construction Services; Design + Planning; Economics; Energy; Environment; Government; Mining; Oil + Gas; Program Management; Program, Cost, Consultancy; Transportation; and Water.

AECOM and its projects have received various awards, including: