The company provides metals processing services and distributes a line of approximately 100,000 metal products, including aluminum, brass, alloy, copper, carbon steel, stainless steel, titanium, and specialty metal products to 125,000 customers such as fabricators and manufacturers.

[2] The company network includes over 75 brands,[3] including Phoenix Metals, United Pipe & Steel, Allegheny Steel Distributors, Best Manufacturing, CCC Steel, Delta Steel, EMJ, Feralloy, Infra-Metals Co., KMS Fab LLC and KMS South, Liebovich, Metals USA, National Specialty Alloys, Pacific Metal, Reliance Metalcenter, Siskin Steel, Tube Service, Valex, and Yarde Metals.

The company was founded in Los Angeles on February 3, 1939 by Thomas J. Neilan.

Originally named Reliance Steel Products Company, the business made and sold steel reinforcing bars (rebar) for the construction industry.

In 1944, the name was shortened to Reliance Steel Company.