Puffing Billy is an early railway steam locomotive, constructed in 1813-1814 by engineer William Hedley, enginewright Jonathan Forster and blacksmith Timothy Hackworth for Christopher Blackett, the owner of Wylam Colliery near Newcastle upon Tyne, in the United Kingdom. It is the world's oldest surviving steam locomotive. It was the first commercial adhesion steam locomotive, employed to haul coal chaldron wagons from the mine at Wylam to the docks at Lemington-on-Tyne in Northumberland.

Puffing Billy incorporated a number of novel features, patented by Hedley, which were to prove important to the development of locomotives. Piston rods extended upwards to pivoting beams, connected in turn by rods to a crankshaft beneath the frames, from which gears drove and also coupled the wheels allowing better traction.