Teesside (/ˈtz.sd/) is a built-up area around the River Tees in the north of England, split between County Durham and North Yorkshire. The name was initially used as a county borough in the North Riding of Yorkshire.

Built-up area
Built-up area's sub divisions
Coordinates: 54°35′20″N 1°11′15″W
Sovereign stateUnited Kingdom
RegionNorth East England
Ceremonial County
Sub divisions
County Borough of Teesside1968–1974
Time zoneGMT (UTC)
  Summer (DST)UTC+1 (BST)
PostcodesTS1-8 & 10-27

The number of people employed in this type of work has declined, steel-making (British Steel) and chemical manufacture (Imperial Chemical Industries (ICI)) and have been replaced to a large extent by high technology science development and service sector roles.