Dorman Long & Co was a UK steel producer and mine owner, later diversifying into bridge building. The company was once listed on the London Stock Exchange.

The company was founded by Arthur Dorman and Albert de Lande Long when they acquired West Marsh Iron Works in 1875. In the 1920s, Dorman Long took over the concerns of Bell Brothers and Bolckow and Vaughan, and diversified into the construction of bridges.

Between 1923 and 1960, the company owned and operated multiple collieries in County Durham.

In 1938, Ellis Hunter took over as Managing Director and he continued to lead the business until 1961.

In 1967, Dorman Long was nationalised, along with 13 other British steel-making firms, becoming subsumed into the government-owned British Steel Corporation. In 1982, Redpath Dorman Long, the engineering part of the business, was acquired by Trafalgar House which, in 1990, merged it into the Cleveland Bridge & Engineering Company in Darlington.

Iron-making has been known in Cleveland since the Romans found iron slags in North Yorkshire, with small-scale iron-making known to have taken place at Rievaulx and Whitby Abbeys and at Gisborough Priory in the 17th century.

Some of the key events connected with iron-making in Cleveland:

1837: The first Cleveland ironstone mine opens, at Grosmont, for the Losh, Wilson and Bell ironworks.