What is the name of the oldest surviving steam locomotive?

The oldest surviving steam locomotive is Puffing Billy. It was constructed in 1813–1814 for Christopher Blackett's Wylam Colliery near Newcastle upon Tyne, England, by William Hedley, Jonathan Forster and Timothy Hackworth.

Puffing Billy hauled coal wagons from Wylam to the docks at Lemington in Northumberland. Its design used two vertical cylinders and gearing connected to the wheels, an arrangement intended to provide enough traction for heavy mineral wagons. The locomotive worked on colliery railways rather than on a public passenger railway.

The title was once associated with Wylam Dilly, a related locomotive preserved in Edinburgh. Detailed examination of both engines in 2008 concluded that Wylam Dilly was built later than Puffing Billy, making Puffing Billy the older surviving example. The locomotive remained in service until 1862, when it was transferred to the museum collection that became the Science Museum in London.

Puffing Billy should not be confused with Locomotion No. 1 or Stephenson's Rocket: those engines are famous for public railway and Rainhill milestones, but both were built later.