ArcelorMittal S.A. (French pronunciation: [aʁsəlɔʁmiˈtal]) is a global steel company headquartered in Avenue de la Liberté, Luxembourg. It is the largest steel producing company in the world and is the market leader in steel for use in automotive, construction, household appliances and packaging. It holds sizeable captive supplies of raw materials and operates extensive distribution networks. The company was formed in 2006 by the takeover of Arcelor by Mittal Steel. ArcelorMittal ranked 74th on Fortune Global 500 list in 2011.

Although official headquarters is Luxembourg (done as part of the deal to merge the two companies), ArcelorMittal is in fact run from London, namely: Berkeley Square House, 7th Floor, Berkeley Square, London W1J 6DA. ("Arcelor Mittal's headquarters may be in Luxembourg, Aditya [Mittal, son of the Chairman] says, but the "power is in London."")

AcelorMittal traces part of its origins to Ispat International, founded in 1976 by Lakshmi Mittal, scion of an Indian industrial family who had decided to build his own business separate from the family, in the form of a greenfield steel plant in Indonesia called PT Ispat Indo. Ispat International became an international company in 1989 when it set up operations in Trinidad and Tobago. Over the next two decades, it has grown through a series of acquisitions in North America, Europe, Africa and Asia. In 2004 it merged with LNM Group (another major steel company owned by Lakshmi Mittal) and International Steel Group to form Mittal Steel Company the worlds biggest steel company. In 2005 it bought Kryvorizhstal for $4.8 billion (twice the market rate) after a bidding war with the then rival Arcelor.