ArcelorMittal, one of the world's largest steel companies, is a joint venture between Arcelor S.A. and Mittal Steel Company N.A. ArcelorMittal is one of the world's largest steel companies, formed by the merger of Arcelor S.A. and Mittal Steel Company N.V. in 2006 and headquartered in Luxembourg. In 2013, ArcelorMittal was ranked 91st in the World Top 500.