Baldwin Street, in Dunedin, New Zealand, is located in the residential suburb of North East Valley, 3.5 kilometres (2.2 mi) northeast of Dunedin's central business district. Guinness World Records calls it the steepest street in the world, meaning no street gains more altitude in 10 horizontal metres (33 ft), measured along the street's centreline.

Baldwin Street runs east for about 350 metres (1,150 ft) from the valley of the Lindsay Creek up the side of Signal Hill towards Opoho, rising from 30 m (98 ft) above sea level at its junction with North Road to 100 m (330 ft) above sea level at the top, an average slope of slightly more than 1:5. The lower reaches are only moderately steep, and the surface is asphalt, but the upper reaches are steeper and surfaced in concrete (200 m or 660 ft long) for ease of maintenance and for safety in Dunedin's frosty winters.

The 161.2-metre-long (529 ft) top section climbs 47.2 metres (155 ft) vertically, an average gradient of 1:3.41. The slope of Baldwin Street is about 1:2.86 (19° or 35%) at its maximum, about 70 metres (230 ft) from the top.

Baldwin Street is a dead-end for cars, but it is linked across the top by Buchanan Street, a footpath following an unpaved road linking it with Calder Avenue and Arnold Street. The streets running parallel to Baldwin are all steep: Arnold Street (1:3.6 or 27.77%), Dalmeny Street (1:3.7 or 27%), and Calder Avenue (1:5.4 or 13%).

The street's steepness was unintentional. As with many other parts of early Dunedin, and indeed New Zealand at large, streets were laid out in a grid pattern with no consideration for the terrain, usually by planners in London. In the case of Baldwin Street (and much of the Dunedin street plan), the layout was surveyed by Charles Kettle in the mid-19th century. The street is named after William Baldwin, an Otago Provincial Councillor and newspaper founder, who subdivided the area.^{[citation needed]}

In 1987, Baldwin Street was recognised as the world's steepest street by the Guinness Book of Records following a two-year campaign by the broadcaster Jim Mora. At the time, Baldwin Street topped two competing streets in San Francisco, which hitherto had held the title of being the steepest streets in the world.

On 16 July 2019, Baldwin Street lost its title of World's Steepest Street to Wales's Ffordd Pen Llech, with Baldwin Street being at a gradient of 35%, while Ffordd Pen Llech being classified at a gradient of 37.45%. Mayor of Dunedin Dave Cull said that the Dunedin City Council could consider altering the signage wording from the world's steepest street to the southern hemisphere's steepest street.

On 8 April 2020, after an extensive review of an appeal to return the title to Baldwin Street filed by several Dunedin residents led by surveyor Toby Stoff, Guinness decided that the steepness of the street must be based on the central axis, which meant that Ffordd Pen Llech had a gradient of 28.6% compared to Baldwin Street's 34.8%. This meant that the title of Steepest Street was returned to Baldwin Street.