Gerdau Ameristeel is the fourth largest overall steel company and the second largest minimill steel producer in North America. Gerdau Ameristeel's common shares are traded on the New York Stock Exchange under the symbol GNA and on the Toronto Stock Exchange under the symbol GNA.TO. The company is headquartered in Toronto, with executive offices in Tampa, Florida.

A historical merger between Ameristeel, Co-Steel, Gerdau Courtice Steel and Gerdau MRM Steel took place in October, 2002. The merger added five steel minimills, downstream concrete products and scrap operations in Canada and the U.S., and effectively doubled the size of Ameristeel, making it the second-largest steel minimill organization in North America. After the successful merger, the new organization took the name Gerdau Ameristeel.

In November of 2004, Gerdau Ameristeel acquired North Star Steel from Cargill, Incorporated, adding a team that operates four steel minimills, three wire rod processing facilities and a grinding ball facility to company.

The company's most recent acquisition closed in June, 2006. Gerdau Ameristeel acquired all of the outstanding shares of Sheffield Steel Corporation of Sand Springs, OK. This added a team of employees operating a melt shop and rolling mill, an additional rolling mill and three downstream steel fabricating facilities to Gerdau Ameristeel.