town and unitary authority, geographic county of North Yorkshire, historic county of Yorkshire, England, on the south bank of the River Tees at the head of its estuary, 7 miles (11 km) from the North Sea. Middlesbrough is the largest town in the Teesside metropolitan area.

When the Stockton and Darlington Railway (Stockton & Darlington Railway) was extended east of Stockton in 1830 to the site where Joseph Pease had acquired land to develop a new coal-exporting port, Middlesbrough came into being; it was the first town in England to owe its existence to a railway. The town was laid out on a regular grid on a site of 32 acres (13 hectares) alongside the new port. The impetus given by the coal trade was reinforced in spectacular fashion after 1850 by the discovery of ironstone on nearby Eston Beacon, and blast furnaces and ironworks crowded into Middlesbrough and adjacent sites alongside the Redcar Railway (1846).

Primary metallurgy has left for spacious estuary sites farther east, but Middlesbrough retains important heavy engineering works. Its port still handles general cargo; and some newer, lighter industries, including telephone equipment, have diversified its industrial employment.

As the Teesside metropolitan area has grown, Middlesbrough has become a regional centre. Additional roads and bridges have been built across the river at Middlesbrough, and the town has emerged as the commercial and cultural capital of Teesside. The shopping centre lies south of the old town of 1830, and Riverside Park occupies industrial sites in the former Ironmasters' District. Area 21 square miles (54 square km). Pop. (2005 est.) 134,855.